Keep line of horizon straight. If not possible then straighten in software.
Avoid placing subjects bang in the center.
Use rule of thirds (divide frame into tic-tac-toe grid) and place most important subjects on the intersection to the top-right: that would be just a bit above right of center.
Use lines to draw attention to the subject
Physical and philosophical repetetitions and patterns are good
Framing using natural available elements is good
Words are too powerful -- if you shoot words then all else will be lost
Fill up your frame. Specially when shooting people get as much of them as possible in the frame.