The first two helpful items that come to mind are:
1) Identify under-tested areas of the specifications and add tests for them.
2) Identify significant CPAN modules and start implementing them.
Please note that the 'identify' steps are important on their own. It could certainly be helpful to have a wiki page about those (If there isn't already one).
I certainly don't have significant seniority in Perl 6, but I remember flailing around looking for tasks when I first started contributing, so you certainly have my sympathy. If you want to know what my personal pet projects I'd like to see worked on are, feel free to contact me on IRC ;) Also, if you ever have any questions about any part of Rakudo, feel free to ask me for help.
If you're particularly interested in helping to work on Rakudo itself, a very good way to get started with that is to spend some of your time reading the commit log as new commits are made and trying to work out exactly what it's doing. That's how I first became familiar with Rakudo and Parrot.