When training with a regular group it's important to know certain aspects of the group to make yourself welcome on the next one. Success is often due to more than fitness.

Know the group's habits.
Some training groups like to go out slow and come back hard. If you're impatient early, you can cause hard feelings by chafing at the bit to go faster. When you know the pattern, it's easier to be patient.

Know what kind of ride is planned.
Will it be a fast training ride? A leisurely spin? Paceline practice? It's disruptive when most of the group is thinking one thing while one or two cyclists are on a different agenda. If an easy recovery ride is scheduled, but you're out for hard training, people are going to get angry. Be certain of the ride's goal before the start.

Know where the ride is going.
Training groups tend to have set circuits they stick too. Its important to know at the start of the ride where you are heading and who in the group has other plans. This is important as some riders may be racing the next day so want to do a shorter ride, yet if you don't know that and get up the road a bit the group may be waiting for them when they have already turned back.

Don't be afraid to say the pace is too hard.
It's a good bet that other cyclists feel the same way but are reticent to speak up - or can't, because they're breathing too hard to talk! Perhaps even the riders who are setting the pace are having difficulty, but they continue to go hard out of vanity or because they think everyone else expects them to. A little communication goes a long way in making a group ride a more pleasant and productive experience.

If you always have trouble holding the pace, look for different group.
Find one closer to your ability level. There's no shame in rationally assessing your strength and choosing cyclists who share it. You'll actually improve faster if you ride with a group that you are on equal terms with. You'll be able to practice paceline cycling, following a wheel, riding in close quarters, cornering in a group, and other important skills.

Don't let group cycling hurt your progress.
Frequently riding with a too-fast group will make you tired. You won't improve as rapidly as you might with more rest. A pace that's too fast will hurt you mentally, too. You'll begin to associate cycling with pain, misery and disappointment. Don't let your ego overpower your better judgment. An appropriate dose of humility now will pay dividends later.

A portion of this material was adapted from: http://avenuecyclery.com/tips/group.htm