her experiences marking targets in instances. There really is an art to laying down those icons in a group, and it requires quite a bit of knowledge to do right. You need to keep group makeup in mind, know the abilities of all the classes involved, pay attention to what individual members want to do and even how they're specced, and have a basic knowledge of the instance and how it works. There's so much that goes into it that it's basically an art in itself -- do you sheep the caster and take out the minions, or focus on the big bad first and then move on to trash? Do you have the group to interrupt and pull a caster to a trap, or do you need to get the mobs out of the way before the patrol comes through?
It's complicated and fascinating stuff, and this kind of group coordination is why some players choose to play PvE rather than PvP -- because while yes, the mobs are predictable (and players aren't; as much, anyway), the fun is in the planning. And when you get a good group to go with a good planner, then things really get interesting. There is an art to laying down marks, but once you study what a good marker does, and get the hang of it, you're that much more helpful to any groups you're in.