I had a longer post written, but somehow lost a good chunk somewhere. Hopefully most of what was lost is still covered.
After arriving at the site, your first stop should be "troll". This is where you'll sign in and pay for the event. Information and a map are also usually found here, as are any rules specific to the site. It is a good idea to know what rules the event is using ahead of time (Belegarth, Dagorhir, or some Realm's specific rules), and read up on any differences between your home practice and the event. When in doubt, ask when you arrive.
After checking in, drop off your gear at weapons check (if it is open). If you haven't already marked your gear in a way you can identify it, do so before dropping it off. Also, make sure they are marked according the rules (like green tape on the pommel for a stabbing sword).
The biggest events are a series of day events strung together with entertainment, feasts, nightlife, and camping. After you are all checked in and waiting for weapons to be checked, it is a good time to set up camp (and change into garb). Most realms/groups camp together. The map at troll often has these campsites marked to help you find where to set up with your group.
Before weapons check closes, there will usually be a variety of sparring, classes, and pick up battles. This is a good chance to fight a few veterans from other realms. If you aren't sure who to talk to, ask a vet from your realm to introduce you to a few people.
After a long day of fighting, there will usually be a Feast provided by the event, followed by any nightlife at the various group camps. To really get a feel for each of the units and realms camping out, you need to go visit their camps. It is best to travel around with a vet that knows the various groups well. Just be sure to say "Hail Camp" as you approach so they know someone is coming to visit. Introduce yourself and hang out for a while.
Sometimes, units will have ceremonies, promotions, and the like. Most of the time, outsiders aren't welcome for them. If they ask you to leave, do so, but don't feel bad about it. They are probably just about to have a meeting or other unit business that doesn't involve you.
A few do's and don'ts of events:
1) DO: Take your hits! I'm required to say that first. Do your best to take them accurately and portray them quickly. If you get confused, just take death.
2) DON'T: Call your hits on other people. It is on their honor to take them (see number 1). If you have problems with an individual, ask a herald.
3) DO: Hit hard. More adrenaline, more armor, and long days of fighting seem to increase people's hit tolerance at events. Shots that might get taken at a local practice may not be hard enough for someone to feel through armor and in the heat of the moment.
4) DON'T: Hit too hard. There is no reason to go at 100% full force on your swings. You want to strike a balance between power and control. Safety is key.
5) DO: Seek advice, training, and sparring during breaks. If you see someone fight well in a style you want to learn, ask them to spar or for some tips. Most veterans are happy to share their experience.
6) DO: Swing!! A lot of fighters find event fighting intimidating. Just go for it. You'll probably die one way or another during a battle, it might as well be while taking someone else out with you.
7) DON'T: Dive headfirst into the enemy. Aggression is good, but carelessly throwing your life away isn't helping your team. Wait for a good opportunity.
8) DON'T: Walk through the weapons check area! You will be yelled at, I promise. Always walk around. We don't want someone getting hit with a backswing because they walked through.
9) DO: Have fun, on and off the field. Even if you aren't winning fights, have a good time trying something fun. Take in the opportunity to socialize with long time veterans and various units.
10) DON'T: Overdo it. Many events are at dry parks, but where alcohol is permitted, be responsible. The last thing you want is to be carried back to your tent or make a terrible impression. Besides, too much consumption will likely ruin your next day of fighting.
11) DO: Be respectful of other camps. This is their home for the week, so respect the rough boundaries around camps and their property. "Hail Camp" before entering their area.
12) DO: Volunteer to help. Events are a ton of work. If you are qualified to help in some way, don't hesitate to volunteer. Even if they don't need help, you can always make sure to clean up your campsite and trash.
13) DON'T: Argue with heralds. Take the hits they call. If you disagree, ask them after the fight.
14) DO: Know the rules. Even vets should reread the rules on occasion. Any rules that deviate from the national rules are likely to be posted at the event. See this post: Unwritten Rules.
15) DO: Sign up for classes ahead of time. All sorts of classes are made available at big events, both for fighting and crafting. This is a great chance to learn from veterans and skilled craftsmen.
16) DO: Arrive early. Try to be at the event as/before weapons check opens.
17) DO: Hydrate! It is easy to forget to take a break and grab some water. I pack a mix of water and sports drinks, along with a few easy snacks.
18) DO: Check your gear ahead of time. Even if you aren't sure how to check weapons, have a vet check your gear a few weeks before the event. This gives you time to make repairs and break in new blades.