Exploit any vulns you can and at low lvl especially that arial assassin's hp pool is small. Targeted damage is nice and frankly absolutely wrecks low hp dexy guys, but there's not much targeted damage in the warriors kit sub-20. Sub 20 I would try strapping on weapons the assassin doesn't learn (flail/mace would be my choice.) and going for bash + rng to give you one or two lucky rounds. That's all you need.

20 or beyond I would go flail or mace first spec and just backhand with charged copper prod or bludgeon with flail.