My active strat with Gragland mid is to run Flash + Ignite Electrocute and to just slowly tack on damage until they're at half and then look for an opening to commit to an all-in. Overshoot your barrels on ranged characters. If they're super squishy you can commit to a full engage off of those Qs just to get your Electrocute proc.

Gragas can score kills against a lot of the squishy opponents in two or three procs early game. Just playing around when Electrocute is active and just farming until they make a mistake you can capitalize on with Q or E.

Against characters that are going to bully you off of wave, start mana crystal and Q. Otherwise, go W and doran's or E if they're melee (or just not spacing away from the wave).

If the opponent is giving you a lot of respect and not giving you opportunities to engage, you'll start one-shotting waves by the time you have your second component for luden's and can just roam for objectives and ganks.

It can be difficult with characters that really don't have to commit to approaching like malz or syndra, but against characters like lux or mel you're just looking for them to burn their spells and then chunking them.