wall of text warning sorry

echoing what [redacted] said, you should probably get 40-50 games under your belt first before looking up guides and stuff, just to get a basic familiarity with the game. i think there was some Go book written by some master that was like "if you have played less than 100 games of Go, put this book down and go play 100 games"
Play 40-50 games, while NOT forgetting to use your potions, and don't forget that "skip" is also an option when drafting cards.
From there, advice gets more individualized but in general:

    Slow down. Take your hands off the keyboard. You are probably bleeding unnecessary health during hallway fights. This can force you to rest instead of upgrade, and being behind by an upgrade can put you on the back foot for the rest of the game. StS is very much about getting ahead of the power curve and using your good position to snowball by taking riskier paths or drafting for the long game. Once you're behind, it's hard to get ahead again. Furthermore, it's difficult to improve your macro (pathing/drafting) when your micro is shoddy, because you might get mixed feedback, i.e. you make the correct macro choice, but mess up your hallway fights and die by playing sub-optimal lines, and then you're left thinking that you made a bad choice in the pathing choice or the draft when in fact it was defensible and you just needed to micro better. Macro takes a long time and lots of experience (because  a lot of it comes from assessing what fights your deck is able to take on and where it needs help, which comes with 100s if not 1000s of hours to be able to eyeball), and so does micro, but to a lesser extent. Remember the chess adage: when you find a good line, find a better one.

Understand the concepts of Front Load, Scaling, Acceleration, and Manipulation. Front Load is a big number on a card, it does a lot of damage or a lot of block (Carnage, Blade Dance, Ball Lightning). Scaling helps you get stronger in longer fights (Demon Form, Dexterity, Creative AI). Meta-scaling cards like (Feed, Alchemize, Genetic Algorithm) help you get stronger over the course of a game. Acceleration helps you play through your deck faster (mostly in the form of card draw and energy generation) (Offering, Acrobatics, TURBO). Manipulation helps you play the cards you want to play WHEN you want to play them (Headbutt, Well-Laid Plans, Equilibrium). There are also sustain cards like Bite, Bandage Up, and Self-Repair that heal you, which can be an important consideration especially when taking Coffee Dripper. Cards can fall into multiple categories, and sometimes in surprising way. For example, Apparitions can be considered front-loaded block because they mitigate an incredible amount of damage, but they are also an acceleration card because they help you play the scaling powers you'd like to play, since you're not having to spend energy on blocking instead. Understanding these concepts helps you evaluate cards beyond "this card does a lot of damage" and "this card helps me block more." It's possible that what your deck needs isn't damage or block, but being able to scale fast enough to beat Champ, or a way to play those key damage cards faster and more consistently. Keep in mind, too, that relics can also fall into these categories. Runic Pyramid is one of the strongest deck manipulation tools in the game, "Ninja Relics" like Shuriken and Kunai help you scale, etc. You can think of card removals as "scaling draw," a form of acceleration that gets stronger in longer fights, as every time you don't draw a bad card, you've effectively accelerated through your deck by that much.

Tighten up your Act 1. Having a good start is incredibly important in this game, and it's hard to give advice about Act 3 because runs can diverge so much by that point. Giving generalized advice is easier in the early game for that reason. This is where drafting according to a tier list can be an acceptable course of action for a newer player. Even if the tier list is only right 60% of the time, that's a far cry better from the beginners' 5-10% hit rate. In very very very general terms, you'd like to be able to take as many elites as you can without dying. Potions are incredibly important for Act 1 elites, and can also be a plan for solving the Act 1 boss. When drafting, think about how each card will play into the three elite fights, as well as the Act 1 boss. Once you've solved your elite fights and have a plan for the boss, it's time to start thinking about Act 2 hallways. Very very very generally, you will draft some early game damage, and then a couple premium block cards, while keeping an eye out for scaling and acceleration. This is extremely general advice and is dependent on a lot of variables, however.

    Watch better players. I'd recommend Baalorlord for newer players, as he's very careful to articulate his thoughts through a run in a beginner-friendly manner (I think he was a teacher at some point or something, it definitely shows). Pause the video when a card reward screen comes up and think about what you would draft and why, and then see what they pick and their justification for it. Jorbs and TerrenceHS also have excellent beginner-friendly educational spire content on YT. This is not an exhaustive list.

Ask for advice in ⁠🧠┊strategy-and-deckbuilding, people are always happy to help and you'll frequently learn something from hearing more experienced players' thoughts on your drafting and pathing choices.