Warning: This may be a tl;dr post!
I've been doing a lot more battlegrounds recently, and although what I'm going to share is probably common knowledge to most people here, it may reach one or two BG neophytes.
First Observation: Communication is Key
It's almost a no-brainer- if there's a half-dozen of the enemy running toward you, then you'll have a faster response when you call out an incoming attack at your location than you will if you don't say anything. Sometimes it can take several seconds after engaging the enemy before the warning "<Insert name here> has assaulted the <insert location>". When you call out incoming attacks, your allies can come to your aid more quickly, preventing the loss of resources.
Communicating properly is also important. Just use the KISS principle (Keep It Simple, Stupid). "Inc <location>" is good. "5 inc <location>" is better, as your teammates now know how many are attacking. It's not just that lone rogue who wants to come back repeatedly and try to sap you and your buddy. Letting them know approximate numbers allows them to decide how many reinforcements are needed.
Communicating things like "WTF guys, we're losing", or "FFS everyone sucks" or "GG defending LM" helps nobody and diverts the team's attention from the objective. Don't be that loser trying to start fights with your own team. And don't be that moron that seems to be in every BG who says, "Oh, let them win, we're going to lose anyway". Especially before the match starts.
Second Observation: Know your Battlegrounds
Another important part of battlegrounds is knowledge of the different BGs. You don't have to be an expert the first time you walk in, but a little research into each one is beneficial. Just going to Alla's Wiki or a website like WowWiki and reading the wikis on battlegrounds (or pvp in general) can give you an overview, and maybe some tips. I also recommend reading For example, Warsong Gulch is a simple game of 'Capture the Flag'. It entails trying to capture the opposing team's flag and bringing it back to your flag spawn point. The first team to cap the flag three times wins. The trick is preventing your opponents from doing the same thing. Arathi Basin is a 'King of the Hill' game in which you have five nodes (or resources) that you try to control. Control of all nodes gives you points faster. The first team to hit 1600 points wins. Eye of the Storm is a combination of both Capture the Flag and King of the Hill. I find EotS to be one of the most frustrating BGs to play, because too many people make mistakes that can be seen in both AB and WSG, and far too often, I've seen half the team rush to capture the flag before any nodes have even been claimed. EotS requires a little more balance than the other two, since one can win or lose based on changes in strategy. Which brings us to my next point.
Third Observation: Strategery!
Yes, I know that was misspelled, but it's my favourite Bushism. Knowing your battlegrounds is one thing. Learning how to strategise is another. People often make posts on Allakhazam (and other forums) about how people run around in BGs like herded cats, or decide to play as midfield avengers in the middle of nowhere, while the objectives are completely ignored.
I'll give a couple of examples of strategy, although these are rather rudimentary and need to be used as suggestions rather than hard-and-fast rules.
My first example is Strand of the Ancients- a BG many people loathe. I hated it at first, but if everything goes right, it can be one of the fastest BGs to do. It's good to start before the match. If you're assaulting you start off on a ship that lands at a beach,and you can choose blue or green. There are four demolishers- two at either end of the beach.Try to get your team to agree on a specific doorway before the boats land. I've found that if the demolishers all try to go to the closest gate (two to blue, and two to green), you're less likely to get through quickly and can end up having to run back multiple times for demos. Also, get melee classes to drive the tanks, and ranged or CC-capable classes to ride in the turrets, so that they can slow down the people trying to destroy the demos. When you're defending, don't ignore the cannons, and take out the demos rather than trying to go head to head with the attackers. A dead demo can't get through the gates.
My second example is EotS. It's a combination of Capture the Flag (on a rock "bridge" in the centre of the map), and King of the Hill with four nodes. I find that EotS, more than any other battleground, requires more flexibility of strategy. Usually, one group hits the western node on your side of the field, another caps the eastern node, and then the third group tries to gain control of the flag spawn point. However, at the same time, you want to try to dominate the field, so there are two enemy nodes that can be assaulted. Leaving a couple of people to call out incoming attacks at each node, a small group can be assembled to attack the opposition. Bear in mind that while you're attacking them, they're probably doing the same to one (or more) of your nodes. Thus, you have to be able to adapt quickly to changes, and not rely on holding two points to win. If you rely too heavily on just capturing the flag over and over, you may leave your nodes vulnerable to attack.
Fourth Observation: Flexibility
This will probably be the shortest observation. Regardless of all of the basic strategies and winning plays that have been used before, there's always a counter to every strategy. If you take three nodes in AB and leave two people at each, you may still lose them if the enemy leaves one at theirs and takes everyone else to assault one of your nodes. If you are in a massive battle at the Stables, that probably means that their nodes are under-defended. Instead of joining the big ugly furpile, it may be a good idea to take a teammate and try to assault one of their bases, forcing them back on the defensive. Life's like a river. Rocks are strong, but water can always flow around them. With enough time, those rocks can get washed away. Fluidity can be good.
Fifth Observation: Leadership
Every so often, you'll get a "leader". It may be a good leader or a bad one. A guy yelling in all caps tends to be bad, in my experience. A person that coordinates well is good (as in, "Group 1 to GM. Group 2 to ST. Group 3 to LM.").
People that try to rally the troops to cap and leave places completely undefended are not good leaders. It's best to leave at least one person at nodes, to call out incoming attacks if nothing else. Personally, I prefer keeping 3-man teams on each base, and letting the rest roam in a group to harass the enemy's bases. If it's AB (with more resources to cap), I prefer lowering the defenders to 2 people if needed, so that you aren't spread too thin. But capping a node and then abandoning it for the next one rarely, if ever, works. All it takes is one enemy to recover it when everyone leaves. But I digress.
A good leader will give clear strategic directions. He should actually know the fundamentals of the battlegrounds. He will be adaptable. He won't just yell at people for "failing", but give suggestions for alternative points of attack, or warn of possible points of weakness. There's also a thin line between strength of leadership and arrogance, but it makes a huge difference between whether people will follow someone's ideas or just ignore him outright. Good direction is admirable. Arrogant dictatorship is not.
Anyway, there's my tl;dr. I hope it entertained someone, and perhaps even helped one or two. If not, at least I know I got a huge brainfart written down!
Edited for clarification & markup.
Edited, Jul 31st 2010 2:53pm by Wondroustremor