Good advice above. I would add the following:
Bring insect repellent, but don't spray anywhere near the scopes. Be sure to ask before using anyone's scope. They will appreciate it. Dress in layers. A hooded sweatshirt is better than a hat, especially if the hat has a bill to get in the way. While you are there, be sure to ask them how they located the particular object that they are observing. Prepare a little beforehand so you know what will be available to see and roughly where to look to find it. No white lights, please. If you have a laser pointer, leave it at home until you get a feel for the ambient club opinion regarding them. Try to get there sufficiently before dark so that you can meet the folks and see their scopes in at least a twilight environment. If the weather crumps, relax and just enjoy checking out the scopes that are there before they get stowed. Everyone is there to have fun, so you do the same. Good Luck and Clear Skies!
ADDED: You will find that some of the members will assume that you have a certain amount of knowledge about scopes or the night sky that you may not in fact possess. They may tend to speak in technical jargon that could leave you wondering what was just said. Don't let them get away with that. If you speak up, they will be glad to explain what they are talking about. They sometimes are just used to talking that way and tend to forget what it was like when they were beginners.