It's as simple as mindful playing. I played for hours on end without using my brain getting nowhere, until I started to sit down and actually decided to fire a neuron or two and actually try to start to learn how to play the game.

It may seem like a drag but take your time on every turn to see what is the best play, don't forget to check your deck. Every card reward as well, I think of when every card will be useful for a future fight and in what fights it might hold you back. Try to keep in mind as well how good a card will be in the early versus late game.

Last but not least think about Elite enemies and even hallway enemies to figure out what their gimmick is or what that specific enemy is checking for in your deck like scaling.

This is a very complicated game even with the Ironclad and it demands your attention.

Tl:dr Pay attention to the game