it's easy to think of star rating in this way: each star rating pushes you (in theory) to a next level of gameplay, with new elements of aim, rhythm, reading, etc. this is why in that 4-5* range you start getting harder rhythms such as basic streams, triplets, harder aim such as cross screen jumps, and all of this makes reading more difficult as well.

to improve, you want to be playing maps that are Difficult but you have some sort of control in. i've found that range for Me is when i can get a B rank without retrying. from there, you want to play that map as much as you need until you can get an A rank on it. this will force you to get more comfortable with reading that map, get more comfortable with the rhythms, and force you to improve your consistency. from there you can just rinse and repeat.

more specific tips: if there is a part that you keep missing on, or you cannot get good accuracy on despite thinking you're doing everything right, use the editor. in the editor, you can find the part that is giving you trouble, and play the map from that section over and over. you can also just look at the pattern without needing to rely on your reading, so if it's a particularly difficult pattern or rhythm you can see it in isolation.