Depending on the champions you are facing with Jax you can either go full aggressive or just play safe back in line. The faster you stack your passive the better, and jax is ready for fight with his R, but dont forget there are many champs that can beat you if you dont play it right. You can kite bad the enemy when you auto x2 and then use Q-auto-W on enemy, that combo is very effective.
Something very good is that Jax can split push very fast and easy,so if you stay behind, you can go side lanes or jungle a bit to gain gold for items.