Get there early to warm up and to get rid of some of the jitters. Bring your gear bag with a cooler and warmer clothing option (I live on the lake, it could be 15 degrees warmer or colder than where the group ride is taking place).
Try not to brake ever (unelss at a stop sign). If you do, signal first.
Keep peddling--you don't want to push hard to catch the group and then coast. This creates a yo-yo effect and everyone has to work harder. You should try to keep a consistant and constant cadence.
Do a short pull at the front when you get there--only 30 to 45 seconds. You don't want to tire yourself out so that you get spit-out the back when you drop.
When you pull out from front, don't make a drastic swerve or sit-up. Keep a steady pace and just ease over. I usually make a signal by tapping my toosh.