I'm stuck at 900 elo

I looked at a few of your games.

When making a threat, ask yourself "what if my opponent sees my threat? Is it still good to put my piece on that square?"

In general a piece is well placed when it's defended, mobile (has many empty squares it can move to) and can't easily be chased away by enemy pieces.

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When your opponent makes a threat, don't respond by making a threat of your own. That usually doesn't work. When your opponent makes a threat either defend or retreat.

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But the most important advice is here, and it's also the most difficult. On every move of every game try to find your opponent's checks, captures, and threats. Before you make your move, find the most annoying / scary thing your opponent can play as a response. If you still like your move, then you can play it. Do your best in every game to not lose anything for free. Not even a single pawn.

And maybe this will be a useful tactic for you to learn. It has to do with lining up your queen (or king) with an opponent's piece (a rook or bishop).

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@1

A rating of 900 is a sign of frequent blunders.

1. Think about your move
2. Decide
3. Imagine your move played on the board
4. Check it is no blunder
5. Only then play it

congratulations on finally reaching your goal

@smokeforce stop playing correspondence chess and you will be there.