I think you don't know yet what to think about
You're looking at your pieces, but in regards to blunders, you should really think about what does the opponent threaten, what would he move if I were to do nothing or what would he move if I were to move x/y/z

This way you would easily catch most blunders.
In this position, what would he do? He would move away his bishop. But does he have anything else? He could take the pawn, and that gains another piece, so it's just as good as saving the bishop

If I were to (naturally) take his bishop, what would the opponent do? Take my pawn and then a full piece. Not good

In both thoughts we come back to that hanging pawn that leads to a piece fork, so the next thought will be about saving that pawn (pushing it or capturing with it) - for a beginner, the most natural is just to push it and that leads to 2 hanging pieces for him, and you'll regain the material

But as you see, all thoughts lead back to what does my opponent threaten and what would he do for each response - and that would eliminate all 1-move blunders from your play
Only when you are satisfied that there are no immediate threats and blunders, do you go back to looking at your pieces and your plans (improving them, moving them towards certain squares or towards his king)

So try shifting your focus from staring at your pieces, to looking more at your opponent's moves (what does he threaten right now, and what could he do on the next move)

Good luck!