- Subscribe to the relevant development mailing lists
- Start using the development version of the software (from CVS, SVN, Git, whatever)
- Subscribe to any relevant community newsfeeds (planets, news sites)
If you're using the development version of software, you'll invariably hit horribly annoying bugs. Dig in, find the fix, generate a diff and mail it to the development mailing list. In the odd case of not stumbling into annoying bugs, the bugtracker will have a long list waiting for you. Rinse, wash, repeat.