You can deter enemies from standing near their minions by setting them ablaze, due to Conflagration.
You can use Brand's abilities in a variety of combinations to maximize his damage in different situations.
Pyroclasm bounces randomly between enemies, so try to cast it on a small group of enemies if you want to hit the same target multiple times.
Brand must land an ability before his combo is able to get started. Dodging his Sear or Pillar of Flame will disrupt his rhythm.
Try to move away from allies when you see Pyroclasm being cast. The initial missile speed is slow, which should give your team time to react.
Brand's passive allows him to excel against teams that cluster together. Be sure to split up against him.