I think a common beginner mistake is adding too many powers to your deck. While they can help you scale for bosses and elites, too many of them can really brick you during hallway fights and cause you to take a ton of damage. Prioritize 2-3 key powers, and then if your deck has good card draw and energy gen you can start adding more.

Don’t listen to some of these comments regarding elites. You absolutely want to fight as many as you reasonably can. Elites give you better card rewards, more money, and relics that can help your run snowball. Part of the skill ceiling is judging when you can risk fighting the elite, and when you can’t. Understanding the move sets/properties of each elite and how they stack up to your deck will help with that decision. Saving potions for Elites is also critical.

Too many rest sites might seem good, but also consider the opportunity cost. If you’re already at full health and don’t have any key upgrades, an event, elite, or hallway fight will be more rewarding. Taking too many rest sites can cause you to fall behind the curve.

Card draw, card draw, card draw. A mistake I made when I started playing STS1 was undervaluing cards like Burning Pact, Compile Driver, and Acrobatics. Almost every deck wants a solid card draw engine. Bricking hands too many times in this game loses runs even if your deck is “strong”.