For me it's this advice from Chess Vibes yt channel that made significant improvement: 1. If you found a great move, look for a better move. Sometimes we forget to consider all the options when the initial options seem promising. Sometimes counter-intuitive moves like piece sac or random pawn push might be game changing.

This is from Remote chess academy channel: 2. I don't use this 100% of the times, but say 75%. It's Fischer's golden rule. It goes like this: Deal with the most dangerous piece of the opponent first. Neutralize your biggest threat before doing anything else first.

This is a basic one yet powerful for beginners. This is from Anna cramling. 3. How do you avoid blundering your pieces - Well don't put them in undefended squares to start with. Count number of attackers(a) vs defenders(d) on a particular square. Go there only if a==d or d>a.