That's a tough one... Find something you're passionate about - something you'd truly like to build yourself. If there's already something on github, join that

That's a tough one... Find something you're passionate about - something you'd truly like to build yourself. If there's already something on github, join that - you can even do a fork first, and play around. Otherwise, just build a new project on github, commit to it, and let people know here/reddit - and see if they'll join