Instructions
Before You Begin
Study an opening and learn to play it well. You might be a whiz at the middle game, but playing the opening poorly makes it hard for you to keep the rest of the game under control.
Learn simple middle game tactics before learning more complicated strategies. Tactics like the pin, skewer, fork and discovered attack are easy to understand and watch out for.
Decide if you like to play open, closed or semi-closed games. You need to know what positions you're good at playing before you can choose a middle game strategy.
Learning the Middle Game
Read one or two books that introduce the basic concepts of the middle game. These should have thorough explanations of strategies as well as sample games that give examples of the ideas being discussed.
Decide whether you prefer to have bishops or knights on the board. The two are generally given the same numerical value, but if you're offered a trade you should know which of the two you want to keep.
Read through a book of annotated games. Mikhail Tal, Vladimir Kramnik, Bobby Fischer and many other top players have published rich collections of their best games that act as great models for how to play the middle game.
Record your games and annotate them later. Try to understand where your games went wrong and why they did, while paying special attention to the middle game and any decisions you made to trade, capture or attack.
Play a lot of chess. There's no good substitute for having match experience even with the support and advice of coaches, friends and books.