Some tactical advices on how to play Gwent in Witcher 3
1. Prepare your deck in advance:
try throwing away all the 1/2 value cards.
2. If you got the weather card in the first cards hand out, leave it only if it doesn't affect the lion share of your squad range type
(ex. you can leave the frost in case most of your squad is ranged).
3. Don't rush putting your highest card on the table. Just firstly check whether your opponent has Scorch.
4. Don't overload your deck with Decoys.
1 (mostly) or 2 are fine.
5. In case your opponent has already passed, play your spy card if you have one.
In this case, they would not be able to take it from the table using the decoy.
6. Don't build your round across only one squad range type.
7. Playing for Nilfgaardian Empire, go with "Emhyr var Emreis: The White Flame" as a your leader card.
8. Playing for Scoia'tael, go with "Francesca Findabair: Daisy of the Valley" as a your leader card.
9. Use decoy to take bake your medic card from the table
to restore one card from the discard pile (like another medic or a spy).