Some addons can be critical in conveying battleground information and should be required, so that everyone is aware of the state of the match at all times. At the very least, the battleground leader should have them. Addons such as Capping Battleground Timers inform you of the map's timers such as flag respawns, node capture times and even estimated time to win in resource maps such as Arathi Basin and Eye of the Storm. These timers are especially important in figuring out how many bases your team needs to capture or defend in order to win the game. Note that the timer jumps forward drastically in Eye of the Storm because flag captures alter the otherwise constant flow of resources.
AlarBGHelper is another battleground timer addon with added features such as announcements on battleground chat, such as identifying the flag carrier in Warsong Gulch or tracking the health of the enemy general in Alterac Valley. The popular raid addon Deadly Boss Mods also has a battleground component that performs similar functions, so there are a few addons to choose from. Battleground chat announcements are almost superfluous with voice communication, but they help keep everyone focused and allow team members to be on the same page without necessarily talking.
Beyond battleground timers, the rest is up to you. Arena target unit frames such as Gladius don't work in the battlegrounds, but I wouldn't be surprised to find addons that will be tailored to the new rated battlegrounds such as honor and conquest point trackers, or even specialized unit frames that allow teams to focus on targets in the battlegrounds. It didn't used to be necessary, but in a rated battleground environment, micromanaging skirmishes becomes far more important.
Get the right mix of classes and specs
It doesn't quite matter in today's battlegrounds, but getting the right combination of specs will become more important than ever. Ending up without a healer can sometimes happen in a small 10-man battleground PUG, but because you can control the group you're going in with, it makes no sense to go without one or more. It's also important to keep track of players' abilities and how they can contribute to team play. As mentioned, death knights and shaman (as well as priests with their Levitate) actually contribute something unique to the team in Twin Peaks. Imagine running the middle of the map as a group carrying the flag -- a team with a death knight with Path of Frost activated can opt to bypass the bottleneck bridge and pass through the sides without the river slowing them down. On the flip side, teams will want a balance druid with the Fungal Growth talent to slow down opponents -- Wild Mushrooms that have an AoE 70% snare can be game-changing in a capture-the-flag battleground.
Unlike battleground PUGs, where players can get away with PvE gear and even raid specs, members of rated battleground premades need to spec the right way because every little thing gives teams an edge. The proper equipment (resilience gear) goes without saying, but it's equally important to choose the right talents, such as Fungal Growth. Blizzard is far from done with the Cataclysm talents and abilities, but right away it's easy to spot abilities that will come in handy in PvP situations. Depending on what finally comes out the gates come Cataclysm, we might even see slight differences in PvP specs for arenas and battlegrounds. Needless to say, you should be speccing for battleground play.
Different abilities come into the fore depending on the battleground. Accelerated movement and snares play a far more important part in Warsong Gulch, for example, than they do in, say, Isle of Conquest. On the other hand, long-range AoE abilities such as the elemental shaman talent Earthquake will be more useful in Arathi Basin as a way to prevent flag captures than it is in Warsong Gulch. These nuances should allow players to shine in particular situations -- it's a wonderful difference to arenas, where the game is all about killing the enemy. Battleground play also focuses on other tasks such as capturing flags, blowing up keeps and killing NPC generals. Needless to say, that last bit requires your group to have someone who can tank. That takes a bit of planning, too.
Practice, practice, practice
The game will change immensely in Cataclysm, and PvP won't be the same at level 85. There is the new paradigm of higher stamina or health for all classes, less burst and less healing. Combat will take longer, be more strategic and require far more coordination. The only way to learn how to PvP in the expansion is to try it -- this means playing the battlegrounds at max level a lot of times. New battlegrounds such as the Battle for Gilneas and Twin Peaks will need to be studied. Optimal strategies for these battlegrounds will only emerge after the WoW community has been playing it for some time.
Take the Isle of Conquest, for example. When it was first released, players headed to the workshop, thinking that control of the workshop that produced most of the vehicles was key to the map. Over time, players realized that Glaive Throwers were far more effective against the gates as well as personnel, consequently intensifying the battle for the docks. Alliance players also learned that they could reach and tag the hangar a few precious seconds faster than the Horde, opening up air drop strategies for that faction. These things are only learned through experience and a lot of battleground play.
Play as a group, play solo ... just keep playing. Being exposed to the whole battleground community can be an eye-opener, especially early on in the expansion. You can count on players to discover clever ways to use new abilities. Learn from them. Read the forums for tips and tricks, scour the blogs (especially WoW.com!) and practice what you've learned in the unrated battlegrounds. Just as with all things, you will need to practice in order to get better. You will need to try out strategies in actual play in order to see if they work. We haven't even learned about the Path of the Titans or guild talents for PvP yet! There's so much to expect when Cataclysm finally breaks out, and it'll take a lot of practice to apply everything. That said, it won't hurt you to start now ... so queue up!