Eight Basic Rules for Writing Cross-Browser HTML Code:
1) Validate the Code. Before uploading your site, you need to check the HTML and CSS code via validators.
2) Try to Keep the Site Structure as Simple as Possible.
3) Do Not Work with Browser Quirks Mode.
4) Use the CSS Reset Registers.
5) Use Firefox.
6) Testing.
7) Use Conditional Comments.
8) Make IE6 Compatible with PNG Format.