Just this weekend, a 48-hour game jam called Bacon Game Jam was held - you can see the games made during that game here: https://bacongamejam.org/jams/bacongamejam-07/games/ , or drop by at #bacongamejam @ Freenode on IRC to say hi!
You can also find general info about game jams here: http://www.gamejamcentral.com/ .
If you have an idea for a project and need feedback or teammates, you can post it on DoerHub.com (it has a lot of university student-led projects with subject matter experts in different areas and people are open to helping/mentoring you when they see you are passionate about learning their craft).
Open sourcing your work is an important part of learning as people will eventually send you pull-requests or report issues to you.
Pairing is one of the best way to get up to speed. Joining a company that believes in pair-programming is important, but you might also want to find a pair for yourself (and open source projects could provide you this opportunity).
plenty of interesting projects to pick up or find someone to work with.
I believe the best way is to create something that you're interested in!