Though more browsers are recognizing JPEG, there are still some that do not. It is best to stick with the GIF format to assure the highest level of compatibility. Again View your page on different monitors and browsers, including the text-based Lynx browser. It should look good, or at least be coherent, on any monitor or browser. Print your page and inspect it.
Many users like to make hard copies of Web pages.
Test your page over a 14,400 modem. Most pages should take no longer than 50 seconds. Under 30 seconds is preferable. Once you have designed your site and it is ready to go public, ask yourself these basic questions.