The Golden Section
Take a square, divide it in half and add the new half to the original square; you have a 3x2 rectangle which is the Golden Section. This has long been regarded as the ideal ratio. It's something art students are taught and most forget. The new wide screen TV's look much better than those old squarish-screen TV's, because they are closer to the Golden Section. Computer screens used to have a better ratio than TV screens. 800x600 isn't perfect, but it's more pleasing than a squarish-screen. Why is this important? Er ... well ... it isn't really; but, if you want to witter on about proportions in art, it sounds impressive. (Coxsoft Art Bullshitter's Guide No 1.) N.B. if you want to be totally confused, click the title link for Wikipedia's definition.