Those are my best tips: https://www.chess.com/blog/tigerchess2022/a-good-guide-to-improve-in-chess
stuck at 400 ELO pls help me
Develop pieces fast, do not hang any officials and lastly learn a proper opening theory and it's side lines, you will be fine.

Improving Your Chess - Resources for Beginners and Beyond.....
https://www.chess.com/blog/RussBell/improving-your-chess-resources-for-beginners-and-beyond
https://www.chess.com/blog/RussBell

The standard list, develop your pieces, castle quickly and control the center of the board. Don't mess around with your queen too much in the opening, develop knights/bishops first. Don't sacrifice pieces. Ignore learning opening theory, just focus on development. 1. Your opponents are not going to know the theory anyways, and 2. opening theory doesn't help much if you blunder a lot, and if you memorise moves instead of understanding the opening's ideas. Just play a lot of chess and focus on not making one move mistakes, instead of autopiloting moves without thinking first. In your rating range every game is a result of one move blunders.
pls help