Few Tips:
After the entrance, there is Millhouse Manastorm and 3 major trash groups. The game mechanics are intended as this:
Pull first group including Millhouse Manastorm. Kill the trash and get Millhouse to 50% hp. Millhouse will than go to the next trash group, rest to full hp. Pull trash group 2, kill trash and get Millhouse to 50%hp. Repeat with trash group 3 and make the first boss spawn.
So here is what you want to do:
You pull group 1, group 2 and group 3 before you get Millhouse Manastorm to 50%. After you pulled all groups, you attack Millhouse to 50% and he will run straight to the rocks and let the first boss spawn. I usually do it this way: I dot Millhouse and use all Movementspeed skills/items to run down. After i reached the last trashgroup, the dots have damaged him to 50% hp and I can move further without waiting. Requires a little timing ofc.
At this time you will be in the tunnel and you have "some adds". Those adds will pull nearly everything inside this tunnel, so there is no reason to avoid the trash inside there... you can start to dot them, but just keep running.
You will now face the boss who dropps the mount and you will still have some adds. Usually, those adds are not right behind you, because most of them are slow.
You want to nuke the boss, before he enters his flightphase, because during his flightphase, he can not be killed. That are some useless seconds.
After you killed the boss you have certain possibilities:
1. You can wait the mobs to reach you, kill them and use the portal to get back to the entrance and repeat the run.
2. The portal works only if you're out of combat. So Hunters and Rogues dont need to kill the mobs.
3. You can queue up for BG/scenario right before you start the bossfight and after you killed the boss, it should pop and you should be able to join, unless there are already 20mobs right around you. Afterwards you can just leave the bg/scenario and you will spawn right outside the instance.
some further information:
- the first boss can be skipped, but i guess that is known
- you can start to attack some mobs while you're running towards the second boss, but you should only do this if it doesnt waste time
- some mobs have their movement speed reduced to very slow if they have 1% hp left. if you're planning to kill all trash mobs after the second boss, you should make sure, that you dont damage them to 1% hp during the run to the boss, because you have to wait additional 20-30 seconds until the slow one reached you