Wave position is not too important. Focus on dodging jungle ganks with your wave position. Try not to push the wave when you are farming with q.

3Q>E max Be unpredictable with your movements so Gragas has a hard time landing his q poke onto you. Take Dshield, second wind, and fleet to endure some of his poke. Stand behind minions and space Gragas’s e since it can combo easily into his ult or q. Use your potion after second wind ends so you get more healing.

Trading against Gragas is not recommended early game. He has so much sustain and can reliably disengage away from you with his e. If his e is down, you could look for an all-in. Post six, bait his q and try to q him through the wave and auto him for the duration. Be ready to dodge his e or ultimate.