I became significantly better at chess through two simple things:

1. Take a little extra time to visualize what will happen after you make a move. Will the piece be vulnerable? Does moving that piece leave a different piece vulnerable? I'd argue the biggest beginner mistake is not seeing that their move leaves a different piece vulnerable to being captured.

2. Don't move your queen into the board until after you move both bishops. This simple rule of thumb makes it far less likely you will lose your queen early, and it forces you to do a lot of other useful things (develop your pieces, control a portion of the board, etc).

Disclaimer: I am not good at chess, but when I played semi-regularly these helped me hold my own against other beginners.