What are some great middlegame chess books that are for beginners that will help me to improve my middle game in chess? There aren't a lot of books on the middle game.
As alluded to in this answer, Seirawan has two useful books that are wonderful for beginners.
Play Winning Chess covers the fundamentals very well, focusing on concepts such as Force (material), Time (tempo), Space, and Pawn Structure. Targeted at the beginner level.
Winning Chess Strategies is the perfect introduction to positional ideas for beginners. Very useful for beginners struggling to find ideas to generate candidate moves. Includes positional puzzles.
Beginners don't really need to understand the middle game. You mostly just need an understanding of basics and tactics to move beyond the beginner stage. Seirawan had a series with a couple of books on the middle game. That's probably plenty for beginners.
Once you start pushing for 2000, Nimzo's My System and Silman's HTRYC are good.
If I were teaching middle-game planning to a beginner, I would just say, pick a target and point all of your pieces at it. The target can be the king or a weak pawn or a hanging piece or whatever. If you don't know what to do, just improve the mobility of your pieces. Most middle-game planning comes down to increasing mobility anyway.