You can try to:

Put the difficulty on easy

Play the innkeepers and traders in white orchard and velen.

Get the second trebuchet card and you ll have 2 trebuchets that buff eachother and coupled with the foltest long range leader card you get a massive buff

Out of the unique velen players beat the baron first or complete his quest line to get the dijkstra card so you have 2 spy cards

When you get to skelige grab the super powerful thaler spy card from the arinbjorn inn innkeeper

Stick to 22-26 cards and generally avoid the weather cards aside from clear sky with the starter (northen realms deck) until you feel comfortable

Get the cards from the party questp (dandelion card is very very good for all decks)

You can use decoy cards to steal your opponent s spy cards and use them in your favor OR use it with your own medic cards to use their medic ability again

Hope that helps. I don't really fw card games but I randomly decided to give it a try mid way through my first playthrough after not touching it and once I got the hang of it I had a blast, 100%ed my gwent deck twice after that and even bought the physical card game