I feel I’ve gone from decent to pretty good just recently, so here’s what I’ve changed recently:

First, and most importantly – think before you act. This was my biggest issue. Just slowing down and not rushing things has made me a far better player in just a few days. I didn’t feel like I was really rushing anything either, but consciously thinking about which cards I choose (and how they interact with my deck and relics), and also which cards I play, has made a huge difference.

Second, keep all your relics in mind. For example, if you have a Kunai or Shuriken that gives dexterity/strength for every 3 attacks played in a turn, try to play three (or six, or nine) attacks per turn whereever possible. On the Silent, having a few Blade Dance makes a huge difference with these.
Build around your relics and their interactions with the cards and they will go from being a small bonus to being run-defining.

Third, look at good players playing and learn from them. Baalorlord is not both perhaps the best player in the world (by the measure of most A20 wins in a row, at 21 wins in a row, all including act 4), but also a great teacher and all around nice guy.
YouTube: https://www.youtube.com/@Baalorlord
Twitch: https://www.twitch.tv/baalorlord

I really attribute most if not all of my recent success to imitating what he does – the other two points are ones I learnt from him.
There are other good streamers of course; I also watched a fair bit of jorbs streaming when I was getting started with the game, which probably helped me a ton with the earlier ascensions, and don’t want to undersell him – he’s also had the world record, probably multiple times.

YouTube: https://www.youtube.com/@Jorbs
Twitch: https://www.twitch.tv/jorbs

Last week I had about 15 losses in a row on A20, with no wins, ever.
Since (and including) my first A20 win last week, I’ve had 6 A20 wins in 13 runs! Three Watcher wins (two in a row!), two Ironclad, one Defect. The most recent Watcher win was also against the heart, which was also the first time I’ve even tried beating Act 4 above A1.

Full disclosure: the stats above exclude all Silent run attempts as I’m still awful with her. Haven’t beaten A18 yet and I’m usually not even close either; frankly I’m not sure how I even got to A18 as I seriously doubt I’d be that much better at 16 or 17.

(This comment is a bit of a test – I can see the threads on lemmy.world but not any comments, so we’ll see what happens. My subscribe has also been pending for a while now.)

Take more combats! Yes question marks are fun, but combats offer you the best chances in the game to add good cards to your deck, get gold, and potions. If you’re thinking long term in the run, it’s almost always better to go for the combat over the event.

Watch at least 1 Jorbs “Overexplained” video. He points out the considerations and calculations you should think about and that sets you on a path to self-improvement now that you know what observations you should be making.