A big help for me was learning gear/items sell for very different prices based on where you're located. I recommend checking a guide for all the ins and outs, but once you reach the main big city, Novigrad, sell most of your weapons and armor there. It's the best place for that stuff unless you have the Blood & Wine DLC.
This goes a long way in optimizing your money to afford the best gear. Then yeah, use the shit out of Quen in combat, apply oils, use potions liberally since they replenish, etc. I think I focused mainly on the attack skills early on, though later the alchemy path has some totally busted builds.
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Welcome to your Divinity.