I've been enjoying Gwent greatly though I'm afraid it's rather distracted me from Hearthstone!
Obviously you can do a quick Google and get good hints and tip - you've already been directed to the Gwent decks site and there are some good Gwent guides on youtube - I found the official guide perfectly satisfactory, and a good place to start:
1: In round one you want to play at least 3 cards, even if you expect to lose the round. The reason being that deck thinning is really valuable in Gwent, by playing out three weaker cards in round 1 you will draw three cards in round 2 that you can expect to be stronger.
2: Don't despair if as a starter you come up against strong recipe decks with big scary cards. The deck building provisions system in Gwent means there's a much leveller playing field between starter collections and big collections. Obviously they will still have an advantage but it's not as big as in HS.
3: Geralt is an excellent starter card (destroys any 9+ strength enemy), but save him for later in the round when you know what the biggest threat is. Also remember that 'engine' cards (cards that boost themselves over time) that are out of Geralt's range at first will come into it later. One other thing about Geralt is that with the occasional exception he's not much use against Nilfgaard decks who usually have mid to low range minions. I mainly play Nilfgaard and have lost count of the number of times I have seen Geralt played forlornly at the end to no effect because none of my minions are above 8. I usually mulligan him if I am vs. Nilfgard.
4: Monsters aren't as scary as they look! As you might expect (given Witcher lore) Geralt is great against them, and they like to play big cards in the last round so keep him around whenever you are vs. Monsters.
5: Against Skellige try to avoid injuring their units because they're a bit like warriors in HS and have a lot of enrage effects.
6: There are some common cards that you really want to play around. Geralt is an obvious one - when boosting a minion try to avoid boosting it to 9 above if you think he's out there. Against Nilfgaard watch out for Sweers and Enslave who can take control of 3 and under units. Enslave can take even stronger units depending on the deck. Also against Nilfgaard watch for Treason (much like Betrayal in HS), I've won a lot of games with Nilfgaard with Treason.
5: You will have figured this out already but for anybody else starting 'lock' effects whilst powerful, aren't as good as HS 'silence' because they don't remove boosts (buffs). To remove boosts you want 'reset' - very powerful, and best left until the end of a round unless you want to heal a key injured unit.
6: Watch for the distinction between bronze cards and gold cards (shown by the colour of the border). When I started I kept being unstuck by this - often a card's power is controlled by only allowing it to work on bronze cards so be mindful of that!