Proportion is one of my favorite ways to create interesting compositions. One good way to achieve an image with great use of proportion is to use a wide angle lens.
This image from St. George Island in Florida emphasizes the sky by placing only a small amount of the green ground in the frame. In this case, the sky is much larger proportionately.
When using a wide angle lens, you can get really close to your subject and make it look much bigger than the surrounding background.
Using this technique and larger proportions in general are a quick and easy way to emphasize a subject that you want to stand out.
Read about the other Principles of Design.