Middlegame training focus is primary to improving one's understanding of chess. Components of middlegame training include tactics, pawn formations, minority attacks, IQP positions, how to handle the center and flanks, and pretty much everything you'll find in any chess strategy book. Today we want to talk about how you actually train and exercise your middlegame brain in chess. Hopefully you do not lack the social skills to enlist a similar or stronger strength chess-playing friend. Otherwise, a competent computer opponent (Fritz 8 or better, perhaps) will work just as well. Freebies like Crafty also are usable.
To be consistent, we will select middlegames that occur out of our opening repertoire. For example, let's assume you play the Caro-Kann, Nd7 variation as black. You are going to want to get the game to a position where one side has several decent choices to make, and set the position there. This will be your starting position for this training session.
Now the fun starts! Playing the side you usually play in that opening, begin the game against your friend. Rapid/Blitz games are good enough for this exercise. The goal of this exercise is to play the middlegame in game situation several times, back to back, and get a feel for what may work and what may not in the middlegame, and also get an idea of what types of endgames you are likely to see. After each game, start again from the same position and switch sides. You'll find that as you perform this exercise, you will be repeating some of the moves and trying different 'improvements' in variations that may not have worked so well in a previous game, and seeing the opening from BOTH sides of the board. You'll become more aware of what practical chances your opponent has in this opening, and hopefully, your partner will reveal some practical advice to you in the opening as well.
To keep things fair with your partner, several games in one variation is enough. Give your partner a choice of variations for the next several games, switching off as you go.
After you do this for a bit, you'll find that you will have a practical knowledge of the transition to the middlegame as it evolves form your opening repertoire. You will also have a practical understanding of what endgames can come about. This is important to know DURING THE MIDDLEGAME as you will then be able to make intelligent decisions on when to trade out to an endgame and when not to.
Chess is about seeing patterns and seeing positions. Seeing these positions stemming from your opening repertoire gives you similar, if not exact, positions you are likely to see in OTB play. Seeing them again in OTB play will allow you to use the already acquired experience from your training sessions to be utilized in your real OTB games. You cannot read that type of knowledge from any book, and that is exactly what training is for!
Note also a side effect of this type of exercise is gathering some opening knowledge as well. Subsequent opening analysis will make better sense as you now have a better idea of what some of the goals of the opening are and how they transition into the middlegame.