1. Keep your code simple as all browsers display simple code the same way (nearly anyway).
2. Validate (check) code as some browsers tolerate errors that others get in a tizz with. http://jigsaw.w3.org/css-validator/
3. Check how your page shows on other browsers http://browsershots.org/ This only does one page at a time with a bit of a delay but it can be useful.
Code downloaded to my PC will be deleted in due course.
WIN7; IE9, Firefox, Opera, Chrome and Safari for Windows; screen resolution usually 1366*768.
Also IE6 on W98 with 800*600 and IE8 on Vista 1440*900.