Two tips for improvement
Firstly, haste makes waste. Hurry is the first and greatest enemy of good play. So if you are about to ping that Submit button, think again. Have you really considered all reasonable response moves? Turn the board around and see the game from the other side. What would you try to do being your opponent?
Secondly, try to gain an idea of your weak points, blind-spots and mis-evaluations. I have a fair idea about my own blind-spots: pins, sacrifices, pieces moving out of the way and distraction of pieces.
My second tip is this: when you do a chess problem and fail to solve it, save the position in a file and come back to it a few weeks later. I have created a file of 182 puzzles that are not very hard but which I failed to solve on the first attempt. I am working through the file a second time and solving most of them correctly.
The idea is to diminish my systematic errors of analysis.