Tougher yet are the mixed bag of ranged attackers and melee grunts. That combo is almost the most deadly thing in the game. Knowing this, you should create your own mix of ranged attackers and grunt attackers. When you see a Mage, you may want to spread your party out, and take cover. Group attacks are a Mage's specialty.
Formations are very important, and so is marching order.
When travelling around on the Sword Coast, be aware that those people in the front tend to get the bejeebers knocked out of them. The T formation is my favorite, with the Fighters up front, Mages in the rear. Now, in a dungeon, it's quite different. It's best for your Thief, in shadows, to be leading. Again this all may seem obvious, but I've seen many an adventurer fall to a group of kobalds, because the monsters were better organized than the party.