When attending a star party, there are a few guidelines one should keep in mind out of respect and courtesy for others. Most are just common sense.
Don't use white lights. Use red lights sparingly. If for some reason you MUST use a white light, shout out a warning.
Make sure you car doesn't violate the above. Backup lights and even interior lights can ruin someone's night vision. If you're planning to leave before dawn, park so as to be able to leave without using your lights.
If you come to a star party without a telescope please park some distance away from the observing site to save room for those with heavy equipment to carry.
Never touch anyone else's equipment without permission. But don't be afraid to ask. Never touch any glass optical surface.
Avoid loud and boisterous behaviour. Astronomy is a quiet, peaceful activity.
Drive slowly so as to avoid kicking up dust.
Watch your step (but don't use a flashlight). Be especially careful of wires on the ground. Some scopes require power and some folks use their car's battery. If your scope requires power try to make the wires as safe as possible.
If you're a visitor or a newbie, try not to monopolize another person's time. The astronomers are there to enjoy the sky, not to give lessons. Except, of course, when the star party is specifically organized for the public or newbies.
Be doubly careful when astrophotographers are doing their thing.
Children -- some folks welcome them, others don't. If you do bring children make sure that they are quiet, careful and act like adults.
Pets -- some star parties ban pets, some allow them. If you bring your pet make sure it is on a leash and under control.
Music -- some star parties ban music altogether, some are less strict. Just remember that music that you love may be extremely irratating to others. When in doubt use a headset.
Alcohol -- some star parties ban it; some almost require it. If you do drink (at a party that allows it) make sure you don't violate the "loud and boisterous" rule. And be aware that alcohol may adversely affect your night vision, body temperature and ability to drive home.
Smoking -- smokers should stay downwind of non-smokers and their telescopes. Just because you're outdoors doesn't mean your smoking isn't annoying, disrepectful and unhealthful to others.