An excellent source of information is The Web Page Design Cookbook by William Horton, Lee Taylor, Arthur Ignacio and Nancy L. Hoft, John Wiley and Sons, Inc., New York, 1996.
Whenever possible, view your website with various browsers and versions, including text-only browsers.
Graphics should enhance a page, not detract from it. (Pages should not have a cluttered appearance.) Many people avoid graphics-intensive sites, or do not automatically download graphics.