The web is a medium that provides a high degree of creative freedom in design and content. Proper site design requires experience and consistent use of basic elements of style and layout.
Style is rather subjective in nature and setting guidelines can seem restrictive.
Many experienced designers have published their ideas on the web and they are well worth browsing. The Yale Web Site Guide is the complete guide to creating effective web sites. The Guide to Web Design by Sun is a compendium of ideas from experienced designers. Avoid gratuitous graphics. Leave plenty of white space.