PEAK by Professor K Anders Ericsson is in a league of its own in the field of self-improving. A lot of this has to do with the fact that Ericsson has dedicated himself to this field for over thirty years. He has made numerous studies which I will talk about soon, but some of you may know about The 10 000 hour - rule which is based on his studies. If not, The 10 000 hour - rule is what it takes for someone to master their craft, everything from an instrument to football, you name it. What Ericsson actually is writing about in PEAK is the truth about The 10 000 hour - rule.
In the book, Ericsson talks about the mental side of mastering a particular subject. How we get better at things like for example chess is because our mental representations get more advanced. This hypothesis did he prove with a study with chess players. He had bad players, average players and master players in the study. What they did was that they put a chess board in front of the players with a specific pattern. Then they asked what the players would have done to win. The bad players had pf course the toughest time because they hadn't seen this pattern before, but the average and master players had. However, the more interesting part of the study was when they just put the chess pieces randomly on the chess board. Then the average and the master players didn't have an advantage over the bad player. This is because was no pattern and therefore no mental representation.
In conclusion, if you want to be good at something you have to practice but also practice effectively. What I mean by effectively is to practice the right patterns. That's why the most effective way to become a master in chess, for example, is by studying the masters' moves.
Disclaimer: He goes more in depth in the learning process, I didn't want to write everything that's in the book. I want you to get the full experience. Here you can buy it.