It is important to farm with Jayce, so make sure you do.

Jayce is good for team fights because when he is in ranged mode he can put down his acceleration gate allowing teammates abilities such as kennan's shuriken to go farther and faster. he can then switch to melee when the team starts to engage.

From what i have seen, Jayce isn't exactly the jungling type.

Jayce's ult is already learned at level 1 and has a 6 second cooldown. It is also good to use your Q and E together while in ranged mode. Your E is an acceleration gate, and your Q is shock blast. When you shoot your shock blast through the acceleration gate, it goes farther, faster, and does more damage.