See How You (Yes You!) Can Get Involved for one good way to help.

I'll also second BUU's suggestion of starting a project on SourceForge (or Savannah for the paranoid). It's a great way to learn while giving something back. As for project ideas check Where the inspiration comes from ?.

This may be blasphemous, but learning new languages is also a great way to gain a broader perspective on programming and can help you better understand Perl.

Update: There's a good article over at perl.com on Becoming a CPAN Tester with CPANPLUS for the interested.