Develop a scale, copy the code, and design your site around it. Scale & Rhythm.
While attending a meeting of one of our local computer clubs, the Design presentation reminded me of an excellent website that provides both theory and tool. Ian Lamb has adapted Charles Bringhurst’s classic book on Typography, “Elements of Typographic Style” for the web. And— provided a tool to test those structures. I love this site. It is beautiful, and useful, not to mention his rather esoteric collection of other fun things.