Instructions
Don't sweat it. It's only a game. The Alliance/Horde WILL NOT crumble if this battle goes sour. Your equipment will remain relatively intact, you will still gain honor and get a commendation, and the world will continue to turn.
Don't swear at people. While you'd think this is obvious, so many people do it when things don't go their way. This is a surefire way to get the troops on your side demoralized, angry and, above all, in the perfect mood to ignore you.
Come up with a plan! Nothing irks experienced players more than a bunch of goofs who sit around with no plan. Think of what has and has not worked for you. Could you have done this better? What if you did this another way? Offer up suggestions! Most people are happy to have almost any plan instead of no plan at all.
DON'T ZERG THE FLAG! In plain terms, this means "do not rush the flag." While this applies particularly to Warsong Gulch, it also holds true for Arathi Basin and Alterac Valley. Running straight up to the flag/resource point and expecting to capture it straight off almost never works. It is a great way to start things off on a bad foot and put your team at an immediate disadvantage. The only way it does work is if your entire team commits to the assault and works together.
Move in teams. Going at it alone is one of the easiest ways to get yourself killed quickly. Ever wonder why the other team scores so many honorable kills? Take a look. 9 times out of 10 it's because they move in teams, assault positions in groups and don't act on their own.
Take and HOLD resources! In Arathi Basin, the idea is to capture and hold strategic resources in order to collect enough resources to give your side the advantage. Quite often, what you'll see people do is run up to a resource (Blacksmith, Lumber Mill, Mine, Stable or Farm), begin to capture it and leave it. Do not do this! This leaves the resource that you may have just fought and bled for completely open for some enterprising enemy to take back unopposed!
Coordinate! One of the biggest handicaps a team can give itself is not to communicate. You have a great advantage real soldiers don't: you can instantly talk to anyone else in your army. So why don't you? Find out where they are. Do they need help? Do you need help? Talk to each other. This cannot be stressed enough! Communication is key!
Be a high level. The battlegrounds are divided by level: levels 10-19 in the first bracket, 20-29 in the next, 30-39, 40-49 and 50-60. A level 12 character will never fight in the same battle as a level 56. What this means is that the level 19, 29, 39, 49 and 60 characters rule the battlegrounds. Wait until you are at least level 17/27/37/47/57 to fight in a battleground (unless you really like getting creamed constantly).