Try to take lots of trades with your corrupting pots. You are quite dominant early, though you fall off a bit mid-game if you don't get kills. You rebound hard late game of course. Ranged champions will have to respect your threat range with your dash, and you can actually zone them off of cs if they know what's good for them. Melee champions are a bit less one size fits all- but W usage is everything. You need to be able to dodge key abilities or use it to mitigate bursts. Against ranged champions, all you have to do is use it to avoid their cc ability, but be careful not to run out of it the second time when it goes away. You can also try to bait the cc ability and then use W to cover your escape and not get poked down on the way out.

You will want to assist your jungler as you are great in invades, skirmishes over crabs and objective fights. You aren't ulti reliant like some other mid laners, and can contribute meaningfully at any time.

Late game, you can either be a second top lane and split push, or you can fight with your team. In teamights, you are a front liner. It seems weird since gwen is squishy compared to other front liners, but with your W you will not be taking damage from the ADC while you have time to kill the tanks/bruisers. If you really need to kill a backline target first, you can try to look for flanks.