All the advice listed above is good and will help you out. However if you are really stuck, roll a Ranger and use Arrow Spray. It is stupid overpowered for a lvl 1 skill and it will hold strong until the end game. This skill can easily kill 2-3 mobs in a single shot when aimed properly. Even if they nurf the damage on the skill its still a really good AOE and will help your other chars make short work of whats left.
