A review and highlights from Peak: Secrets from the New Science of Expertise by Anders Ericsson, Robert Pool (ISBN: 0544456238).
For a good criticism, see The New Yorker article Practice Doesn’t Make Perfect by Maria Konnikova, 2016-09-28. The main point being that there is a lot of research indicating that practice only accounts for a part of performance and natural predisposition is also important.
For me, as an aspiring martial artist, this was one of the two revolutionary books of utmost importance (the other being Ralston’s Zen Body-Being). It explores how we do acquire skills - and what is the most effective way to do so. The book distills the key findings of the past few decades of the new science that studies top performers in various mental and physical fields. Based on these, it provides practical guidelines for creating the most effective practice.
A key claim is that innate talent is of little or no importance in the long run1. The only factors important for your performance are the amount and quality of your practice. And the quality of it makes a huge difference. You can easily waste a lot of effort with limited results - or proceed at top speed. So what makes for a high-quality practice is what we will look into.
The most effective way to acquire any skill
It turns out that “just doing something” (i.e. “the usual approach” or “naive practice”) doesn’t help us to improve after we have mastered the easy stuff2. The most effective way to learn - and keep on improving - a skill is “deliberate practice.” The more applicable “purposeful practice” is deliberate practice lacking the optimal, experience-based guidance:
Deliberate practice is purposeful practice that knows where it is going and how to get there.  Deliberate practice develops skills that other people have already figured out how to do and for which effective training techniques have been established. The practice regimen should be designed and overseen by a teacher or coach who is familiar with the abilities of expert performers and with how those abilities can best be developed. 
So what are the key components of purposeful (and thus deliberate) practice?
So here we have purposeful practice in a nutshell: Get outside your comfort zone but do it in a focused way, with clear goals, a plan for reaching those goals, and a way to monitor your progress. Oh, and figure out a way to maintain your motivation. 
- Purposeful practice has well-defined, specific goals. It
is all about putting a bunch of baby steps together to reach a longer-term goal.
- Example (music):
Play the piece all the way through at the proper speed without a mistake three times in a row.Without such a goal, there was no way to judge whether the practice session had been a success.
- Example (golf):
What exactly do you need to do to slice five strokes off your handicap? One goal might be to increase the number of drives landing in the fairway. That’s a reasonably specific goal, but you need to break it down even more: What exactly will you do to increase the number of successful drives? You will need to figure out why so many of your drives are not landing in the fairway and address that by, for instance, working to reduce your tendency to hook the ball. How do you do that? An instructor can give you advice on how to change your swing motion in specific ways. And so on. The key thing is to take that general goal—get better—and turn it into something specific that you can work on with a realistic expectation of improvement.
- Example (music):
- Purposeful practice is focused. Give the task your full attention. Be aware of what and how you are doing and how it differs from a good/better/ideal way of doing it.
- Purposeful practice involves feedback. You have to know whether you are doing something right and, if not, how you’re going wrong. Without feedback—either from yourself or from outside observers—you cannot figure out what you need to improve on or how close you are to achieving your goals.
- Purposeful practice requires getting out of one’s comfort zone, i.e. trying to do something that you couldn’t do before, something just beyond your current abilities - while focusing on exactly how you are doing it, where you are falling short, and how you can get better. This is perhaps the most important part of purposeful practice.
But sometimes you run into something that stops you cold and it seems like you’ll never be able to do it. Finding ways around these barriers is one of the hidden keys to purposeful practice. Generally the solution is not “try harder” but rather “try differently.” It is a technique issue, in other words. [..] it is useful to work with a teacher or coach. Someone who is already familiar with the sorts of obstacles you’re likely to encounter can suggest ways to overcome them.
- All obstacles can be passed:
In all of my years of research, I have found it is surprisingly rare to get clear evidence in any field that a person has reached some immutable limit on performance.
Thus it demands near-maximal effort, which is generally not enjoyable.
- (Maintain motivation. Get internal or external meaningful positive feedback, make sure to get enough sleep and keep healthy, take breaks etc.)
- Deliberate practice requires, in addition to the points above, a field with clear best performers, understanding of what they do to excel, and knowledge of how to best develop these abilities. And a coach that can apply this and, among others, can develop a plan for making a series of small changes that will add up to the desired larger change, tells you also particular aspects you should be paying attention to, what errors you have been making, and how to recognize good performance.
Feedback is crucial but how can you provide feedback to yourself? You need a good enough “mental representation” of the activity. For a physical skill, this is an understanding of and “feel” for how it should be and (for example in terms of body positioning and momentum). Coupled with focus and awareness, it provides an understanding of what and how you are doing so that you can notice and try to correct your deficiencies. Thus you can both get a feedback and keep improving your mental representations:
Early in the training process much of the feedback will come from the teacher or coach, who will monitor progress, point out problems, and offer ways to address those problems. With time and experience students must learn to monitor themselves, spot mistakes, and adjust accordingly. Such self-monitoring requires effective mental representations. Deliberate practice both produces and depends on effective mental representations. 
Good mental representations are crucial for any skill:
Much of deliberate practice involves developing ever more efficient mental representations that you can use in whatever activity you are practicing. 
What sets expert performers apart from everyone else is the quality and quantity of their mental representations. [..] These representations allow them to make faster, more accurate decisions and respond more quickly and effectively in a given situation. 
I would thus conclude that effective practice requires that you are aware of and deliberately work on improving your mental representations, whether your skill is more mental or more physical.3
My key takeaways
- What constitutes an effective practice (specific goals, feedback, focus, …)
- The role and importance of mental representations
- I have to experiment myself to find the most effective training techniques to address a particular weakness for myself
- Be analytical: dissect the skill I am trying to learn, understand its components and which give me most trouble so that I can address them effectively:
To effectively practice a skill without a teacher, it helps to keep in mind three Fs: Focus. Feedback. Fix it. Break the skill down into components that you can do repeatedly and analyze effectively, determine your weaknesses, and figure out ways to address them. 
- Take the time to identify those aspects of performance that I would like to improve and then design training methods aimed specifically at those things
Additional quotes of interest
As we shall see, the key to improved mental performance of almost any sort is the development of mental structures that make it possible to avoid the limitations of short-term memory and deal effectively with large amounts of information at once. 
In short, the human body is incredibly adaptable. It is not just the skeletal muscles, but also the heart, the lungs, the circulatory system, the body’s energy stores, and more—everything. 
As demonstrated e.g. by Minoru Yoshida of Japan did 10,507 pushups nonstop. Some changes that may occur: change in the metabolism of the muscle cells, changes in their structure, and a change in the rate at which new muscle cells were formed; an increase in the amount of myelin around nerve cells that can increase the speed of nerve impulses by as much as ten times; the area of the brain that controls the fingers of the left hand has gradually expanded, resulting in a greater ability to control those fingers. (Though an extraordinary development in one area is often correlated with regression in another one.)
As long as the physical exercise is not so strenuous that it strains the body’s homeostatic mechanisms, the exercise will do very little to prompt physical changes in the body. From the body’s perspective, there is no reason to change; 
Indeed, one could define a mental representation as a conceptual structure designed to sidestep the usual restrictions that short-term memory places on mental processing. 
the key benefit of mental representations lies in how they help us deal with information: understanding and interpreting it, holding it in memory, organizing it, analyzing it, and making decisions with it. 
Effective mental representations can also guide you in finding or creating the most effective practice techniques for the type of difficulties you experience.
The Top Gun approach to improvement:
In the early days of the Top Gun project, no one stopped to try to figure out what made the best pilots so good. They just set up a program that mimicked the situations pilots would face in real dogfights and that allowed the pilots to practice their skills over and over again with plenty of feedback and without the usual costs of failure. That is a pretty good recipe for training programs in many different disciplines. 
If you find yourself at a point where you are no longer improving quickly or at all, don’t be afraid to look for a new instructor. 
It is better to train at 100 percent effort for less time than at 70 percent effort for a longer period. Once you find you can no longer focus effectively, end the session. 
For everyone who faces a plateau:
the best way to move beyond it is to challenge your brain or your body in a new way. Bodybuilders, for instance, will change the types of exercises they are doing, increase or decrease the weight they’re lifting or the number of repetitions, and switch up their weekly routine. Actually, most of them will vary their patterns proactively so they don’t get stuck on plateaus in the first place. Cross-training of any sort is based on the same principle—switch off between different types of exercise so that you are constantly challenging yourself in different ways. 
This, then, is what you should try when other techniques for getting past a plateau have failed. First, figure out exactly what is holding you back. What mistakes are you making, and when? Push yourself well outside of your comfort zone and see what breaks down first. Then design a practice technique aimed at improving that particular weakness. 
Bloom found a slightly different pattern in the early days of the children who would grow up to be mathematicians and neurologists than in the athletes, musicians, and artists. In this case the parents didn’t introduce the children to the particular subject matter but rather to the appeal of intellectual pursuits in general. They encouraged their children’s curiosity, and reading was a major pastime, with the parents reading to the children early on, and the children reading books themselves later. They also encouraged their children to build models or science projects—activities that could be considered educational —as part of their play. 
Then he was inspired by a paper that described a training technique that had helped musicians without perfect pitch learn to recognize a single note. Brady set up a computer to produce random pure tones—these are tones that consist of a single frequency, unlike a note from a piano, which has a dominant frequency but also a number of other frequencies as well—and he used those pure tones to practice. At first, he had a large percentage of the randomly generated tones at the frequency of a C note, theorizing that if he could learn to recognize the C, he could use it as a base from which to recognize the other tones by their relationship to the C. Over time, as he got better and better at recognizing the C, the computer was set up to generate fewer and fewer of the Cs until all twelve notes were being generated with equal frequency. Brady spent a half hour each day training with the tone generator, and at the end of two months he could identify every one of the twelve notes being played without error. 
[..] I can report with confidence that I have never found a convincing case for anyone developing extraordinary abilities without intense, extended practice. 
Recent research has shown that children who have had experience playing linear board games with counting steps before they start school will do better in math once they are in school. 
a new approach to teaching physics that Wieman and others had developed by applying the principles of deliberate practice. For one week they had the students in their section follow a very different pattern than in the traditional class. Before each class they were expected to read assigned sections—generally just three or four pages long—from their physics text and then complete a short online true/false test about the reading. The idea was to make them familiar with the concepts that would be worked on in class before they ever came to class. (To even things out, the students in the traditional class were also asked to do preclass reading during this one week. It was the only change made in how the traditional class was taught during that week.) In the deliberate-practice class the goal was not to feed information to the students but rather to get them to practice thinking like physicists. To do that, Deslauriers would first have the students divide up into small groups and then pose a “clicker question,” that is, a question that the students answered electronically, with the answers sent automatically to the instructor. The questions were chosen to get the students in the class thinking about concepts that typically give first-year physics students difficulty. The students would talk about each question within their small groups, send in their answers, and then Deslauriers would display the results and talk about them, answering any questions that the students might have. The discussions got the students thinking about the concepts, drawing connections, and often moving beyond the specific clicker question they’d been asked. [..] The students in the Deslauriers class were getting immediate feedback on their understanding of the various concepts, with both fellow students and the instructors helping clear up any confusion. And both the clicker questions and the active learning tasks were designed to get the students thinking like physicists—to first understand the question in the proper way, then figure out which concepts are applicable, and then reason from those concepts to an answer. [..] Wieman’s achievement is tremendously exciting. It suggests that by modifying traditional teaching approaches to reflect the insights of deliberate practice, we might dramatically improve the effectiveness of teaching in various fields. 
For instance, it has always been surprising to me when I talk to full-time athletes and their coaches how many of them have never taken the time to identify those aspects of performance that they would like to improve and then design training methods aimed specifically at those things. 
When preparing a lesson plan, determining what a student should be able to do is far more effective than determining what that student should know. 
Most people, even adults, have never attained a level of performance in any field that is sufficient to show them the true power of mental representations to plan, execute, and evaluate their performance in the way that expert performers do. 
1) For example, perfect pitch - the ability to recognize tones perfectly - is not an innate talent:
While in normal circumstances only one in every ten thousand people develops perfect pitch, every single one of Sakakibara’s students did. (Though
In the case of perfect pitch, it seems that the necessary adaptability in the brain disappears by the time a child passes about six years old)
2) This applies in general, here one specific example:
Research on many specialties shows that doctors who have been in practice for twenty or thirty years do worse on certain objective measures of performance than those who are just two or three years out of medical school. It turns out that most of what doctors do in their day-to-day practice does nothing to improve or even maintain their abilities; little of it challenges them or pushes them out of their comfort zones. 
3) In an experiment, those who practiced basketball throwing physically once a week and mentally for times a week exceeded in performance those who practiced only physically (or only mentally). I suspect that is because they essentially worked on their mental representations.