Why are you not improving?
It could be a number of different things. Are you analyzing your games after you play? Are you reading chess instruction books? are you a diamond member on chess.com where you get free instructions and a lot more awesome tools this website offers? Or do you just play every day or a few games a week and expect to suddenly get better?
Chess is a very difficult game and you must put in the time to study classic games and see the reasons behind every move. There are plenty of books out there for beginners but honestly the reason you are not improving is most likely because you are not studying the game and trying hard enough.
Hard work is required, but in chess in particular, I think you can make the mistake of directing a lot of hard work to the wrong area. In particular, a lot of raw beginner players (<800) do the right thing when they start, and make huge fast gains studying tactics, tactics, tactics, but then stall out when they expect that same study strategy to continue gaining them points at OP's level (1200ish).
In contrast, if your study is directed to your problem areas, it can take dramatically less work to have a substantive impact on your rating. Again, I do think that in the absence of a coach who can pinpoint your problem areas AND provide effective ways to improve them, studying full annotated games is one of the best ways to naturally get at this.
Tactics is actually the easiest skill to get 'up to par' for your rating. Most lower-rated players at OP's (or my) rating, lose a lot of games due to a late-game tactical oversight and blame it on 'I keep hanging pieces', when in reality, they were making small positional and development errors repeatedly that made it not only possible, but sometimes easy to blunder in an inferior position. So the big error isn't 'hanging pieces', but allowing such a position to arise in the first place, and studying more tactics will only make a minimal difference in preventing these 'blunders'.
Why are you not improving?
It could be a number of different things. Are you analyzing your games after you play? Are you reading chess instruction books? are you a diamond member on chess.com where you get free instructions and a lot more awesome tools this website offers? Or do you just play every day or a few games a week and expect to suddenly get better?
Chess is a very difficult game and you must put in the time to study classic games and see the reasons behind every move. There are plenty of books out there for beginners but honestly the reason you are not improving is most likely because you are not studying the game and trying hard enough.