Get the lay of the land. When you arrive, step to the side. Take a deep breath and scan the room. This will give you a chance to regroup and focus before you approach anyone. Stay in control of who you talk to and for how long.
Also, don’t sit down right away. Wait until the program begins. If there is no program, you can sit once you’ve connected with someone. Because you’ll appear more approachable, you’ll have better opportunities to meet people while standing.