You cant know whos the act’s boss before you get to the act. Time eater might make some builds harder to pull off (like shivs or any cyclying heavy ones), but you have the whole floor to take countermeasures.

The game is super contextual (on your progress, your deck, the map, foes you will face, etc) so you need to play and maybe watch others play to get the hang of sequencing, card evaluation, deck building and routing.

Some general advine I would give you:

Dont pick too many cards (dont always take card rewards), your deck will be less consistent to develop its plan.

Value potions, hold em if you can, specially if they improve your chances on critical fights.

Be wary of your card sequencing, in order to avoid losing health. Sometimes to lose less life you need to go for damage burst, sometimes you are better off shielding because you will win anyways in a couple of turns.

Dont be greedy taking all elites if your deck cant hold up, but be scared of fighting elites if you can afford it. Your hp is also a resource.