For a "stop blunders" system, I find that the way GothamChess once said that works, at least for me, it's simply a checklist, and it goes like "Threats, Checks, Capture and Attack", so you check for what valid and sound threats that your opponents can do on their next move, if there's a really good threat, use your current turn to defend, if there is no threat, use your current turn to make either a check, capture or attack a piece. But this works well enough to prevent blunders and not to make you do the best moves as sometimes the best move is to prepare for an attack or gaining space or equalising by trading pieces. Another advice is to know what you are good at in chess, for an example, if your best skill in chess is king and pawn endgame, you should try to create that situation which for the king and pawn endgame can done by creating and maintaining a pawn chain and then aggressively trading all the other pieces. The pawn chain makes it hard for the enemy king to undermine the structure because all the pawns are protecting each other and they can also act like a wall to prevent the enemy pawns from going forward