My suggestion to go along with depth of field is rule of thirds.

Your main subject should never be placed dead center, you loose everything around it. If you just move it to a side or up or down, it draws your eye to everything around the main focus.

This should be done too before cropping, the best photos don't need to be touched up.

The last photo accomplishes this because the main subject is the women. She's off to the side and you see the dog in the water and the fish, but you always keep coming back to her.