3. If a bug has already been filed for what you want to do, check its [[Bugzilla:Priority_System|priority]].
4. Write some code. Make sure that you follow the [http://www.bugzilla.org/docs/developer.html Developer's Guide]. If you're new, you don't have to read the whole thing. Just read the [http://www.bugzilla.org/docs/developer.html#general General Guidelines], the [http://www.bugzilla.org/docs/developer.html#perl-style Style] section, and any other part that you think applies to the code that you're writing.
5. Test your patch. Make sure it works, and run ./runtests.pl in the Bugzilla directory. Also use [http://validator.w3.org the HTML validator] to make sure your code generates valid HTML, if you modified any of Bugzilla's HTML.