There are many excellent books on the middle game in chess. One highly recommended book is “Positional Decision Making in Chess” by Boris Gelfand, a former World Championship challenger. This book covers various aspects of the middle game, including pawn structures, piece placement, and prophylaxis. Another great book is “Build Up Your Chess” by Artur Yusupov, which offers a comprehensive study of the middle game with many practical exercises.

“Mastering the Middlegame” by Grandmaster Nikolaos Ntirlis and “The Thinkers” by David Llada are two other books that have received high praise for their treatment of the middle game. Grandmaster Davorin Kuljasevic has also authored several books on the middle game, such as “Chess Middlegame Strategies Volume 1-3.”

In addition to books, there are also online courses available that cover the middle game in depth. One such course is the “50 Middlegame Masterclass” on Chessly.com, which features video lessons by International Master Levy Rozman and annotated games to help improve your understanding of the middle game.

To improve in the middle game, it is essential to study various aspects such as pawn structure, piece placement, and tactics. It is also crucial to understand the strategic ideas behind each move and to be able to identify critical moments in the game. Developing a strong positional sense and the ability to evaluate positions accurately are also key skills for success in the middle game. Regular practice and analysis of games are also important for improving your understanding and skills in the middle game.