I was unsure whether this question was about joining a long term closed group of swingers such as Numex and herpob have, or joining a group on a much more short term basis.
I had a girlfriend that liked to play, and the first encounter we had with others was an eight-some at the red rooster in Vegas, followed by a six-some on the same trip. We were soft at the time, but nobody was disappointed at our performance!