Keeping it Simple
Before you trip the shutter, stop for a moment and evaluate the image you are about to take. What is it about the scene that interests you? What in the frame isn't relevant to the message your image conveys? Don't try and include everything in your image; a cluttered frame can lessen its impact.
If you can recompose to remove as much extraneous information as possible you will end up with a stronger image. You can do this by cropping tighter from your current position, or by changing your perspective by moving your position.
Try to simplify your compositions. You should end up with more of what interests you and less of what doesn't and your images will have more impact as a result.