Do it alone.
This might seem hypocritical considering my previous blog post, but do things alone. Don't wait for others to join you. It just becomes another form of excuse that prevents you from doing what your heart yearns for.
If you want to go to the gym regularly, it's good if you can find an accountability partner. But you shouldn't be counting on it. You should be willing to do it all alone.
If you want to go running or join a new sport, let your friends know, but don't be dependent on them for doing the activity.
One of the things that I did after joining college is to try out new things regardless of my friends' interests. If I were swayed by friends' interests at that time, I wouldn't have joined the debate club or started running, for that matter.
So go out and do things that excite you.