I agree that volunteering is a great way to meet people and to "give back", which makes YOU feel good too. I volunteer at the local therapeutic horseback riding center, working with horses and disabled children and adults. It's wonderful - so much so, that I am now studying to become a certified therapeutic riding instructor ... something I never would have done when I was drinking! I'm also going to be volunteering at the local animal shelter soon.
Exercise helps ... so do creative things that you can do with your hands (and they help you get out of your head too). I'm learning how to quilt after wanting to learn for many years. So far I suck at it, but I'm enjoying it.
You can also look into clubs that do things you like - sports, music, books, etc. Or if you want to learn a new skill, look into classes in your area ... I'm going to be taking a gourmet cooking class this summer. Stuff like this is a great way to meet people who share common interests.