It will work out best if you can find a genuine passion, interest, work-related problem, or itch to scratch, and choose a project that is important and interesting to you.

The (now inactive) Perl Phalanx project showed that without a genuine reason to work on a project, folks tend to lose interest after a while and stop contributing.

If your goal is just to improve your Perl by practice, see Re: Real Life Perl Exercises, a comprehensive list by planetscape.