While the standard answer is "practice" - that word needs some defining if you're going to improve as much as possible.
Practice does not mean turning up and shooting a certain number of arrows or for a certain length of time.
Practice means methodically working on and improving all aspects of your shot: posture, grip on the bow, draw, anchor, release, follow through and more.
Find (either from input from a coach or by videoing yourself) something that needs work and then work on it until the improved form is second nature. Then move on to something new.
This approach has served me well so far (I'm in my 9th month shooting now) and I think it should work for anyone from the casual shoots-only-for-fun archer to the type who takes it a bit too seriously (me).
I'm starting to work on being more methodical still now, doing some non-bow exercises (stretch bands, straps and the like), mental exercises and so on... but this takes a bit more time and dedication. Not so much the shoots-for-fun archer shouldn't do it or wouldn't benefit from it, but enough that some might not want to put in the extra effort.
Good luck.