At your level, choose a move that makes a threat above one that doesn't, all other things equal. This will screw up your opponent more then defensive moves.
But honestly, this probably isn't your problem at an 800 rating. You can reach a 1400 rating just by rarely leaving a piece undefended, being able to spot one move checkmates most of the time, and being able to see when a piece is in a position to be taken (en prise) most of the time.
Attacking or defending really puzzled here need urgent help?
please answer me!