Considering I just recently got into PVP, I'm hardly an expert. But I thought I'd spend some time clarifying some misconceptions I had before I dived into the pool head-first.
It takes no skill to Battleground PVP. I had the conception that it was akin to a raid in an instance, knowing one's class, and capability, having the gear, and being able to use all three in a quick fashion. I found I was mistaken, to a great degree. It is simply a "dive in and slaughter" situation. Get off as much as you are capable of, as quickly as you can, and adjust as you go. If you've ever tried to get spells and attacks off, following a level 70 around as a lower level in an instance, it's similar to that. Quick, find how hard you can hit something as quickly as you can. And if you can hold it in place, do so, or help the others to do more damage, or barring that, to not let it hit you and kill you. A no-brainer. This is why the 'BG twinks' are so effective. Highest level gear/ench/materials to throw on themselves and beat others with. Being at the level cap for the particular BG is best if you want to have the least amount of pain and most amount of kills. Levels 19, 29, 39, 49, etc.
If you're lucky, you might have a BG Leader that has a strategy. Usually, you do not. It's simply actions that everyone 'generally' takes to accomplish the goal of the game. You will be automatically grouped if you don't have one, or if you join as a group, you will be in party already with that group you had as you all joined in the BG game together. You do not have to stay with your group, or even attempt to. No matter what you do, your group will help you to gain honor and kills. So it's not just your fighting that matters, you can get bonus for healing too, as well as bonuses for capping a base, or killing a mob. Pray for a level-cap member in your particular team, or a BG twink
It's usually a very good idea to stick to -some- group or another, less likely to die if you have others helping you beat on whatever is beating on you.
You must get adjusted to dying. A lot. You are rather quickly resurrected (15 secs)at a pre-destined area (generally whichever area your faction currently controls) and you take only minimal durability damage when being beat on or being killed. You will drop "insignias" to be used in the BG itself with vendors in your home area to gain reputation and faction rewards. I find that a little hard to do with having 2 minutes to the end of a game. And you can get special points for achieving special activities in the spanse of the game you are currently in. Overall the object is, dying less, having more kills and killing blows than the others.
You have four battlegrounds from which to pick, depending on your level.Your level will match you to players from all across the servers a battlegroup of similar level. So there will be Level 20-29 players, for example, in a BG together. This can be fun or painful, depending on your style of play, and capability. Nothing like being on the low end of that stick and beating on the high end twink that just found you
Wait times to join the BG vary on how many have signed up across the servers to join in the battle. You may 'que' for as many BGs at a time as you like, and it will remove you from one BG to another if you are currently in one and choose to 'join another' from another que. (It is important to note however that you will not gain honor or marks from a BG that you leave for another, you simply will not be stuck with the 'deserter' flag if you take that route.) The fastest que is usually the current Honor Holiday BG. The * in a name/guild title denotes a player from another server. It will appear as (Bob-Stormrage) in the channel.
You -can- cross-server ignore and report. Reporting most behaviors in a BG is a waste of time, as well, it's there to cause you pain. Expect it. Do not AFK in a BG if you can help it. It is a reportable offense and it will get you a deserter flag. You will also occasionally be reported (in a harassment fashion) for such a thing unfairly, especially if you're -really good- at PVPing and are stomping someone flat. Make certain to explain to the GM if you are ever dumped out like that, what your suspicion is. If you choose to 'leave a battle', you will be flagged a "deserter" and will not be able to join another BG for 15 minutes. If you choose to 'leave a que', you will not be flagged for anything and simply can move about your business. There will be a mini-map icon once you join the que, and again, when in the BG for you to use for information. There are addons to help gauge BG progress and such, but I have no idea what they are. Others have them, and usually report on channel. So watch for those things on the "Battleground" channel.
Warsong Gulch is a flag battle. (It is the earliest accessed BG.) The intent of the game is to get the flag of the opposing faction and return it your faction's base. Now, this can be painful, as it's a game of 'beat the geek' when you have the flag, and also they tend to
not to turn in the flags. (Called 'turtling') I believe it's 3 flag returns to make a winner. It's within a certain time frame, thankfully, but still, it can be rather unpleasant if they turtle. I find this to be the longest and sometimes most painful of the battlegrounds.
Alterac Valley is a 'cap the towers' battle. The intent is to cap as many of the opposing faction 'towers' (buildings) as you can, as well as kill their leader (at the opposite end of your map). Generally, this is the easiest place to farm up honor, as it's a massive cluster of death and destruction in a path. You also kill mobs along the way, or have mobs kill you. Capping an opposing faction's tower sets it on fire, and doesn't allow you to reclaim the tower. Whomever has the most towers and resources left by the time limit is the winner.
Arathi Basin is a resource gathering battle. You have areas to collect and defend, and it's the most 'ditch battle' style battleground. You basically attempt to take, or hold, a flag. You can also help to widdle down the resources by killing the mobs that spawn when you do not have a flag at an area. It has a time limit, and it goes by rather quickly. If you have teams and they have a strategy you will be fine. This is the most common face-to-face fighting area. I prefer to defend a flag, than cap one, but both can be fun.
Eye of the Storm is like a mixture of Warsong Gulch and Arathi Basin. You have four towers to cap and keep, and a flag in the center to grab and return to the nearest 'tower' under your faction's control. It's also set up so you can see the nearest two opposite areas clearly, as well as the flag. Watching for invaders is really easy that way. It's really a great deal of fun and seems to have the most likely chance of having -of-similar-level- people in with you. Turtling is not possible with that flag, and generally the object is forced to make them turn it in as quickly as they can, so you get more points. Really fun BG.
All in all, it really takes no time at all to gather honor and marks, so in a way it's really the best option for a player who wants an 'easy' epic item or mount. You get three marks and more honor for a win, and one mark and regular honor for a loss. You get double honor for a win on a 'holiday' weekend, which is heralded by the particular faction wandering your hometowns on the weekend. (IE: League of Arathor, or Defilers)
You can enter the various BGs from one of three places. -Your capital city's collective, IE: Stormwind in Stormwind Keep has the four battlemasters standing together in the War Room.
-The BG entrance itself. IE:Alterac Valley can be accessed from the actual entrance to the battleground (which used to be the only way to approach it) from behind Hammerfall. You will find quests for the BGs at these entrances, whereas they are limited elsewhere.
-The Faction heralds for the holiday weekend. They will allow you to join the battle from wherever they are wandering at the time, for that particular BG.
The only other notes of worth I can think of: Watch other classes like yours. Emulate them, or learn what -not- to do. Focus on your strengths. If you can't spaz-twitch pvp, then perhaps defense would be a better option for you. Take fun items with you, such as
potions of detect invisibility or
goblin landmines. They can be your friends and the one or two things that keep you from dying. Listen to the raid channel so you can hear 'the plan' if there is one, and if there isn't, suggest ones you've heard before that will work. You might be able to make your team's win happen. Expect to have jerks who camp you, your graveyard, or sneak and hit you dirty as they can. (Such as the sheep/kidneyshot combo of the mage/rogue that I was hit with for one entire battleground as my mage...) Expect that they'll whine that you're losing or that you suck and shouldn't ever play. Don't bother asking where you should go to help, divine that for yourself, and make it happen, because otherwise they'll say 'go level', guaranteed. Ignore the chatter for anything but useful information like "Inc Farm" or the like. Make sure to use the channel to state incomings, or losses, to help your team out. Stun, root, blind, beat on and otherwise mutilate your opposing faction. And most of all....
Have fun! 
