One of the most commonly neglected aspects of design that I see is negative space. It's the space in your design which contains nothing. It may be white, black, or could even have a background of some kind, but visually it is empty space. The modern trend in design seems to be to put in everything but the kitchen sink. This isn't however the best way to get your point across. Consider one of the masters of negative space, Michelangelo.

Why does this image invoke such emotion? I give you a clue... Negative. Space. The careful use of negative space draws the eye and increases impact. So next time your working on a design, pay attention to the space you use, and the the space you don't.