Mhh.. hard to describe the way how I find the motifs for my pictures. I find them and know if it's something special or not.
In case that I think it's worth to take a picture or a stack I try (if possible) I play a bit with the composition. Should mean that I try to place the insect or the mushroom to the left or to the right or I try to add elements like moss, branches or things like that.
There are for sure some general rules like to set the focus on the eye(s) or the pollen stem of a flower but it depends what I want to show.
It's mostly a good idea to respect the 1/3 rule but it should be no mandatory.