One simple thing I have found to be very helpful is to spend a lot of time actually playing the piano.
I know that sounds silly, but what I mean is to play some pieces that are at your level, some slightly below your level, and a few just slightly above your level.
That way you are spending a lot of time playing, rather than slowly learning a difficult piece, or working on a technique exercise.
The playing reinforces what you know, and gets you used to playing in a comfortable and low-pressure format.
Its kind of like learning how to ski...you can read books, watch videos, but actually getting on the slopes is where the learning is...but make sure you spend your time on slopes at your competence level! That way you enjoy it, and get used to it, and thus pave the way for improvement.
This does not mean that you also do not work on a piece of music that is a bit above your level, so you are pushing the envelope, nor does it mean that you are not doing exercises.
I have personally found this very beneficial, and use it with many of my students.
One caveat: Whatever you play, try to play it well...Sometimes I find myself getting sloppy because I know a piece. I don't know why that happens, but it does.
Music teacher and piano player.