Here are a couple of things I can think of:
1. Try to make keep the horizon level. If your camera has different marked focal points in the viewfinder, you can use them as a guide.
2. BlueJay mentioned the Rule of Thirds a while back. It has to do with putting your main subject off to one side or the other, not perfectly centered. Google it. I did and think it helped my pictures.
3. try adjusting the contrast a little, if you have the ability with your editing tool.