I will be adding to this build. Updates to come.

Nautilus's damage output isn't the biggest, but he makes that up with being pretty tanky and having a lot of crowd control. He works best in a teamfight, so don't solo with him.

Before jumping into battle, use your W to shield. Then open with Q, followed by an auto-attack (to immobilize) and then E to damage/slow. By now your Q should be close to being able to use again. Rinse and repeat.

For your ultimate, try to target a champion behind another, so that the shockwave knocks both of them up.