Make it clear. Use diagrams and images and pictures. Make pages load fast and you'll make me happy. If you must use pictures, please assume that I don't have much bandwidth. Life is slow on the Internet.
Life is very slow.
I don't care that your system is fast and your connection is fast. I don't have your machine or your connection. Whenever possible, be consistent. Don't get cute or fancy or tricky. It is all right to bend the rules sometimes, rarely, since I don't want every site to be the same.