How to break through 1500 elo

I'm currently stuck at 1500 elo rapid for about a month and can't quite figure out how to improve.

Firstly, although I learnt relatively much theory I couldn't quite put them into practice and couldn't make a clear-cut plan for me and prophylaxis my opponent's plan.

Secondly, it's hard for me to find the difference between good players(like 1600-1800elo) and very good ones(2000+) except for some inaccuracies and strategic mistakes. Thus I don't know where should I try to breakthrough.

If anyone has ideas for chess development please comment below, thanks a million!

@1

"can't quite figure out how to improve"
++ Analyse your lost games and learn from your mistakes.

"I learnt relatively much theory" ++ Useless.

I would say doing puzzles maybe a start as theory is to much, learning simple tactics may help