Our goal is a 2.2.1 RC release containing important bugfixes and django 1.4 compatibility.
The relevant issues have been organized into three milestones on github.
Have a look at the open issues and find one you feel comfortable solving. Then contact one of the core devs to claim it. We'll then tag the issue as claimed and add [claimed by @username] to the description.
Make a feature branch and start coding. Don't forget tests ;-)
Make a pull request to the develop branch on divio/django-cms. A core dev will review your pull-request, give you feedback and eventually merge it.