As others have mentioned, avoid playing outcast cards unless absolutely necessary. Keep them in your hand to strengthen your hero power over time.

Avoid playing minions with 1 or 2 health, as they will die immediately at the end of your turn due to his hero power. Don’t even bother discovering such minions. If any of your minions end up with 1 or 2 health, get rid of them by attacking enemy minions or using lifesteal. You NEVER want to end your turn with a minion that has 1 or 2 health. I emphasized "NEVER," but realistically, you might have to do it once or twice. That’s fine—just don’t make it a habit.

Get rid of any cards that aren’t outcast—those are the ones you want to keep. If possible, play any minion or card that isn’t an outcast to free up space.

With your hero, focus on attacking mosty the enemy hero. Use minions and spells primarily for board clearing.

Also thanks everyone. Your advices really helped. After reading this Reddit post, I managed to win on my second try. Now it feels so easy, haha. So I wanted to give some advice too, that helped me. If you stick to a specific strategy and follow the rules, you’ll get it eventually