Starting Items and Early Game

Doran's Ring + two pots into almost every matchup. The mana sustain is critical since Q costs mana and you'll throw it a lot early while you're learning the arc.

Play safe until level 3. You have no kill pressure without E reset. Farm under tower if needed. Don't trade without Q landing first.

Diana's level 6 is one of the hardest spikes in the game. If you're even in CS at 6, you win almost every 1v1 in the midlane. Start looking for the all-in the moment R comes online.