1. Validate it with w3c : http://validator.w3.org/
w3c is the standard of the web

2. Make sure that it works fine with most of the browsers. ou should at least test it with Mozilla Firefox, Opera and Google Chrome. Apple’s Safari uses the same engine as Chrome but you might check that as well. Additionally alert the viewer that IE is not fully w3c compatible thus should be replaced with other browser. Keep in mind that IE is getting better and better.

3. Install Mozilla Firefox and addons firebug, web developer, noscript
Firebug allows you to trace how the page is loading

4. Optimize your pictures – pages with huge background images (sometime >1MB) could be often optimized (the same pictures could be <30kB)

5. Follow the w3c path – and check your page with multiple browsers (you can find some unsupported w3c features in almost every browser)

6. Keep in mind that browsers can lack the support of : javascript, java applets, clickonce, silverstream, flash, frames, …

7. If possible – avoid animations when not needed and do not use sounds

8. You can add some way for the people to grade/comment your page. People would probably only say that the page is bad. They might give you the reason. Usually no one would spend more then couple of minutes to tell you what is wrong with the page.

Last and most important: Test, test and… test