Let the group know that you are ready
When you see a mob, pause and make sure that everyone is ready, especially if it is a large group of mobs.
Choose the highest level mob and mark it, as that is the one that you need Cabal Alz to go for. Let the group know that you are ready, and then head in for your kill.
Use all your skills and abilities as a tank to kill the most powerful mob there. The others in your group will start picking off the others, or helping you with the one you have chosen. Once you slay that mob, move on to any others that are left standing.
Make sure that you help to slay any mobs that are left so they don't hurt your other group members too much.
If an item comes up that is green, blue, or purple, and is one that you either need for a quest or that you can use or wear, it is always polite to ask if you can “need” the item instead of just doing it.
More than likely, it won't be a problem, but there are always those few that will gripe about people needing.