@synposis #1:
I see myself in your post. You said you end up just defending and reacting to your opponent's moves, and this is me exactly. I really struggle to take the initiative and try to launch attacks, instead just becoming obsessed and paranoid about defence, no doubt seeing "phantom" threats that aren't really there.
It seems that I'm around your age (give or take a few years), and I started playing chess a couple of years ago. For what it's worth, here's my experience and advice, which has got me to 1500 classical:
(1) Play long games. I'm truly terrible at bullet and blitz, but much better at classical. Have you got time, say on the weekends, to play a 45+45 or 60+30 game? Give yourself time to think. It can be hit and miss finding an opponent for these longer time controls, but if you can, the games can be really worthwhile. (You may already play such games, so if you do, disregard this) :)
(2) Do a "blunder check" before each move. Before moving a piece, ask yourself:
- Am I moving the piece to an undefended square? Can my opponent just take it?
- What am I "undefending" by making this move? For example, suppose my queen on d1 is the sole defender of one of my knights on b3, say, and suppose my opponent has a rook on b8 attacking the knight. If I move the queen to d2, say, the knight is losing its defender, and my opponent may be able to take it.
- Following this move, has my opponent got any checks? If so, can I deal with them? Is my opponent threatening to capture anything? If so, is it adequately defended?
- Am I leaving myself vulnerable to any forks, pins or skewers?
(3) Further to this last point, familiarise yourself with potentially dangerous alignments or configurations of pieces. For example, your king and queen lined up on the same rank or file could be vulnerable to a skewer if your opponent can get a rook to that rank or file; two rooks line up on the same diagonal could be skewered by a bishop.
In particular, watch out for knight forks; learn the configurations of two pieces which could lead to them potentially being forked by a knight, and look out for these patterns during your games: for example, two pieces at the opposite corners of a 4x2 rectangle, of a 4x4 square, of a 5x3 rectangle, on the same rank or file with one or three squares between them could potentially be forked by an opponent's knight.
If any two of your pieces are arranged in one of these patterns, make sure that you're aware of it, and before each move, ask yourself whether your opponent can exploit it.
(4) Be aware of the coordination of your pieces; try not to have your pieces and pawns getting in each other's way.
(5) Watch your pawn structure; try to avoid having doubled pawns, isolated pawns, etc
(6) If you haven't already, watch John Bartholomew's Chess Fundamentals and Climbing the Rating Ladder videos on Youtube; they're brilliant, and helped me a lot.
(7) Lastly, and most importantly, enjoy your chess. At the end of the day, regardless of whether I win or lose, if I enjoy a game, then that game was worthwhile. I'm never going to make master level, or anything remotely close to it, but I hope I never lose the enjoyment that I get from chess. Whether you're rated 900 or 1900, have fun.
Good luck in your chess journey :)