Focus on getting stacks with your Ult by sending the enemy to Hogwarts. Q is there for bursting down enemy. Once you get Surge of Power imbued to Q you can play a bit more aggressively. You can also optionally focus on camps and split farming with Monster Rounds, and periodically pick off people with Ult. Collect as many trophies as you can and recruit as many people to Hogwarts as you can!