Originally Posted by Allegheny Jet

Most groups would welcome you into the fold, provided they feel comfortable with your bike skills. If you wish to join the group announce yourself, get on the rear and stay there for a while, watch the dynamics and chat with some of the riders. After a while, if you are comfortable with the pace, move up into the group and eventually take your share of the pulls.

Remember, every group is different and is riding for different reasons. You may or may not be welcome if the group is on a base ride and you hammer the pace when pulling or your bike skills are twitchy and they don't feel safe with you there.