My advice is to get a well regarded book on one of the following topics:
tactics, endgame, or strategy.
Then play over every line of analysis in the book on a board and take notes as you go. After setting up a position try to figure out who is better and why. What move would you make? Then play over the book's moves. You can also pause at any interesting moments in the middle of a line and do the same thing. The point is you should interact with the material. Don't just passively play over the moves.
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If the book is tactics it's a little different. My advice is to set up the position and then (unlike online tactics) do your best to solve it without moving any of the pieces. When you think you have a solution, write down your solution using chess notation, maybe even write which side is up material and how much.
You should be close to 99% sure your solution is good, but even so, now look over your line for different moves the opponent can try to refute your solution. All of this still without moving the pieces.
After that you can check the real solution. Any puzzle you get wrong make a note of it, wait a few days, and try it again. It's important to retry puzzles like this until you get them right at least once on your first try.
It's also important to figure out why your intended solution was wrong. Using a chess engine is helpful.
So, I've been been stuck around 1240-1330, and I don't know what to do. I've been analyzing my games, and it seems like I always do something that weakens my position, not in an immediately noticeable way. but it eventually leads to a loss. Anyway, I'm getting sidetracked. I assume that "Studying chess" would get me out of this whole, but I'm not sure how to go about doing this. Any tips?