For your first group ride, I would recommend going on an organized no-drop club ride, not the Tuesday Night World Championships. Let the ride leader know it's your first group ride. You'll probably be asked to hang out at the back to see what's going on and get comfortable. Make sure you keep your head up and look through the rider you're drafting. Protect your front wheel, don't overlap. Cover your brakes, but don't use them unless necessary. Hold your line. Don't allow gaps to form. And above all, be smooth.