-Have plenty of defensive structures in your base and teleport the opponents to your base. The towers will kill the enemies before they can do much damage. The Convert spell will also work, because they are free men.
-This strategy works best with the elves. To kill armies (including brutal) easily, first get as many Mirkwoods as possible. Have them guard your fortress and make sure they get Silverthorn Arrows. After that, get Glorfindel and Arwen and three to five groups of horses. Upgrade them fully and then send them around the back of the enemy base. Have them attack. This will work almost every time. Make sure that Glorfindel and Arwen are on their horses. It also helps to have Rally Call and Heal.
-Use the following tactic on the Minis Tirith, Minis Morgul, Helm's Deep, or Isengard maps. Build your army and close the gate, then place three battalions of Archers on the walls of both sides of the gate. When the enemy starts attacking, kill them. You can open and close your gate rapidly from time to time to taunt them. When you open the gate they will try to enter but your archers should take care of them.