One of the best ways I've found is to volunteer your time. This makes sense for a few reasons.

A. The people you are with are also likely volunteers (opensource, event/meeting organizers, etc), which means you will meet people with a favorable attitude/mindset/values. The people with the most to give are the ones with the most value.

B. You have the same interests as them.

C. Volunteers are commonly a very diverse spread of people (experience/jobs/projects/goals/etc).

D. Meeting people like this makes it easy to keep things casual, or move into a partnership type relationship.