The same goes for banner graphics. A good header GIF for a page should never be any size larger than 20k, and that's still pushing the envelope. Always add ALT tags to your images, so the browser knows what each image is. A user should have all the important information in front of them. Also, if you must use background images, make sure that they are small and contrast well against the page's text.
Ugly backgrounds are the hallmark of bad web designers.
Make navigation simple. There should be links to most of your site at the top of each page, and again at the bottom in the case of larger pages. This keeps every bit of content you have within easy reach of the user. Organize your site into as many top-level branches as necessary, to allow the user to get what they need in two or three clicks. Programs like FrontPage, Hot Dog, and PageMill are not substitutes for good HTML skills.