This is how you start. This is by no means where you'll end - you'll need to make sure you're a reasonable distance from each other because there are plenty of things that will force you to move around, then find a new position.
1. The bite - On 10-man, the second air phase coincides with the time needed to find your bite target. That means it's imperative that you both bite someone _and live through the bloodbolt whirl_. This is difficult, yes - but if the healers stay still and bomb heals during the bloodbolt, and no one stands too close to each other, you should be fine. Should be.
2. Pact of the Darkfallen (AKA "The High Five" or "The Red Line"). The reason we leave the middle open is because that's the high-five zone. When we're in 25-man and have three of them, it's even more important to keep it open and to keep the debuffed people healed. Follow the line, and if you're near the line you should step back a bit (in 25-man, just meet in the middle - don't try and follow the line, since that'll just get confusing).
3. Legion Flame You do not want to make a U shape with your flame - run out to the wall, stay along the wall, and _when you stop leaving flame_, run back in and find your spot. It's tempting to run into the next open position in the circle, but all that does is trap people. Make a direct line to the wall, then start moving along the wall.
4. Air phase terror - This is the most important one to worry about and the cause of the most wipes. The cooldown on air phase is 2 minutes, and this makes it perfect for wearing a pvp trinket or using your Human racial - you get more active time to spread yourselves out again - healers should stay still as long as they can to keep the heals up, as it's VERY easy to lose people to Bloodbolt Whirl at this point. Everyone is responsible for themselves, of course, but healers have the hardest job here, so it's good to have them stand still until she lands, at which point you start phase 1 again.
5. Air phase terror + bite - Actually, it's THIS combination that causes the most wipes. At this point, the melee will run up to the tanks (in 10-man) and bite them, while the DPS will be biting a healer (usually). This makes for very very difficult healing, and this is what cooldowns like Paladin sac, Paladin bubble, shield wall, shadow ward, etc. will be useful for. Do everything you can to keep yourself alive while biting your next vampire target, and the 8-vampire phase SHOULD be a breeze.
Let me know if there are any questions about the diagram above and about other kinds of movement.
