How do I become better?

I'm a new chess enthusiast, but I don't seem to be better than when I started 3 months ago. I know a little bit about openings, but after that I'm lost. I have no clue what to do in the middlegame, I usually just improvise, then most often lose in the end.

I would really like to know if there are any books you would recommend on the middle-game for beginners, or just must-read chess books in general? (But not too high level)

Also, are there any specific "drills" I should do daily? I solve puzzles sometimes, they seem to make me better at puzzles, but not chess.

PS: Been looking at the book "My System" by Nimzowitch. Do you think it is appropriate for me?

I think it might be helpful to look at a book like Simple Attacking Plans by Fred Wilson

https://web.archive.org/web/20140708090402/http://www.chesscafe.com/text/review874.pdf

or The Most Instructive Games of Chess Ever Played by Irving Chernev.

https://chessbookreviews.wordpress.com/tag/most-instructive-games-of-chess-ever-played/

My guess would be that it is probably best to postpone the readimg of My System for now, but, for what it is worth, here is a review.

https://web.archive.org/web/20140708105648/http://www.chesscafe.com/text/review600.pdf

Tactics trainer helps. Initially the best plan is to improve your worst piece. But tactics really help improve. Also study basic endgames

@Hanz202

I'd recommend "Chess: 5334 Problems" by Laszlo Polgar.

Also Wikipedia has an article about Checkmate Patterns that may be of use.

If you lose most of your games in the endgame that is definitely the place to put your effort; and the tactics trainer.