Good text legibility requires high contrast, and in general black text on a white background provides that better than any other combination. In particular, remember that visual acuity for blue is poor, and that blue text on a black background will be hard for everyone to read. Color images on the web should be designed for use in a 256 color environment. This is more restrictive than it sounds, because Netscape and other browsers generally allocate a specific set of 216 colors for presentation when the overall system color depth is 256. Color images should be reduced to this palette before being used on the web.
Many people use tables for layout.
There can be drawbacks to this, and some techniques will help minimize the risk. Always specify widths as percentages, and never use absolute pixel counts. Summary Sites may fail for a variety of reasons, but most come down to inexperience with the environment, or forgetting about one's readers. The fundamental solution is to make a commitment to your readers to provide the best web page possible. This site also includes an excellent list of HTML validators.