I watch tutorials posted by reputable streamers.
I also like to create weird (often weak) decks to play in casual, to see what I can do with them, and what opponents do when pushed out of their deck’s routine plan.
Surprisingly, I have probably learned more from a “mindless” monsters pointslam deck than anything else. The beauty of pointslam is that it places a premium on passing, pushing, and bleeding — aspects of Gwent that are unique and subtle.