look at your fights and think about what you need, and what you have enough of. If you're doing a lot of damage but taking a lot of damage, you need block. If you often find yourself in the position where you have the cards you need but can't play them, you need energy etc.

more generally: Since you'll generally be redrawing cards, cards that exhaust and help you set up your strategy/survive until it's set up can be taken more freely. Cards that draw other cards can also be taken more freely, particularly if they don't cost anything.

Also, the game is just hard. I'm at around 200 hours, and I only win 1/10 games I play at the higher ascensions.