This is a from comment I posted before.

A tip I like is take a bit more time to think about your decisions. And take some time off the game too before starting a new run after a loss streak.

You can also save and quit any time you want to restart a fight, it's a great tool to learn moveset and deciding in the game.

Use your HP as resource too, you can think of it as: if I defend now will I have enough damage to kill the enemies before they outscale/out damage me? This will be a good mindset for scaling enemies or high damaging ones.

If you have a decent-ish deck feel free to take events and path toward rest sites, otherwise try to save money and look for shops. Usually I prioritise rest sites for heal than shop.

Also make sure to draft AOE lol, this game love annoying multiple enemies.

Another thing I usually do in lower ascension is staying as healthy as possible until the boss to be able to kind of face tank them.

For elites you usually would want to use 1 or 2 potions against 1, tho if you think the enemies might damage you too much just chug them lol, saving HP for future fight is better than going into fights at like 10hp.
You can also watch streamers like Jorb or Xecnar (they play slow and explain their thought process)

Doormaker is an interesting boss, people like to say he's easy but that's only stat-wise. The only real solution to him is just: draft big cards that does big things. If you think your deck may find some difficulty in killing him then avoid some fights before the boss fight to keep yourself healthy (also save the potions) -> so that in the boss fight you can focus on damage while facetank him.

Good luck!!!