Strong diagonals and composition
 

I notice that some paintings I have seen here use strong diagonals going directly into corners. If you can offset these diagonals so that they miss the corners, you will, I think, have a better composition.

I have illustrated this below in the most simple way I can think of:

The first illustration is static as the diagonals bisect corners.

This second illustration makes for a better composition as it misses the corners and offers better shapes.