I too am a novice, but here is what I do;
approach the circle with your drum, and listen to what they are playing. Watch the circle, and try to determine who the "main" players are. These are usually the ones that are doing most of the "solo" playing or keeping the beat steady (usually up front with most of the drummers watching them). Wait for several minutes without sitting down or playing, just listen and groove for a few while watching the main players.
At some point, one of them will make eye contact with you, and "invite" you in and maybe indicate with their eyes were you should sit (maybe so they can keep an eye on you) . Either that or one of the outer players will invite you to sit down and play by them.
Start slow with the basic beat, wait for it, and soon you will be totally inside the circle jamming away. Just don't try to take over the beat (try playing softly if you have problems at first). I just play the basic rythm, try to learn all the basic parts, before I start trying to solo, but my friend (who is REALLY good) just makes eye contact and starts to answer calls.
Talent hits a target no one else can hit; Genius hits a target no one else can see.