How to play middle game?

this pertains primarily to the middlegame...
Good Positional Chess, Planning & Strategy Books for Beginners and Beyond...
https://www.chess.com/blog/RussBell/introduction-to-positional-chess-planning-strategy

Well activate your pieces, castle...
Then it pretty much depends on the given opening, the pawn structure, and the reaction of your opponent. Sometimes you have mini goals you want to achieve, like controling a square, or developing a badly placed piece... Or attacking on the kingside... And your opponent tries to prevent that...
There are different plans for different positions. Check out some strategy books (like Silman) or videos.

My personal solution was to play for imbalance and then the game came naturally with respects to planning, positions, tactics, counter play and end game.
Thanks, guys I think now I understand it isnt so simple, I also have some books to read and I'll look into those. I think I have an aggressive play style, but with a kind of sharp defense so, I'll try to play with that in mind.

I just love your optimism... for me, just getting to middle game within 3 points of equality is enough to make my day...

Rule #1 of middle game play is to not make bad moves.
Rule #2 of middle game play is to make good moves.

In seriousness, the middle game is characterized by lots and lots of possible lines. Play accordingly.
1. Calculate everything.
2. Because you can't calculate everything, improve characteristics of your position. Look at pawn structure, pins, forks, outposts, bishop pairs, open vs closed, any advantage that could be useful beyond the horizon of your calculations.
3. Protect the king. It's most vulnerable in the middle game.
4. If you ever calculate a win, take it. But don't force something that's not there. There's not urgency like in opening and end game.
You don't necessarily need "plans." What you do need are "ideas."
I would like to know the general idea of what to do in the middle game after you have taken control of the center. This will help me not only play the middle game, but choose a good opening.