Scouting out the group first can really help. While it's always good to burn down the easy guys first, you can make your life a lot easier by initially charging a ranged mob. The melee at that point, if there are any, will always run to you, so you can usually group up at least some of them that way. Even if they're weak, I'll never go for melee first, since I'd lose that opportunity to bunch them up a little.