Largest technical problem for me is that I tend to raise the fingers that do not play too high. My thumbs look kind of funny sometimes. I think this habit started when I played a lot keyboard in various pop/rock bands. As the keys are very light, you cann afford to rest your fingers on the keys as that will press them down. Another problem I have is a stiff right hand wrist. That is my worst problem as it cause pain which in extreme cases has lasted 1-2 weeks. I had a severe problem practising the 8:th prelude of Chopin a couple of years ago. I injured myself so badly (over-practise) that I had to take a 4 weeks rest and I easily regain this problem.
Trills. Between my 2nd and 3rd finger. I know, that should be the easist, but I tend to trill too fast with these fingers and the result is an unclear mess. I trill better on the other fingers. I need more concentrated practice, more discipline, more yelling at myself to stop and spend extra time on trills practice.
Normally I have loose wrists so if I raise a hand while playing that the hand falls down. Also the fingers are curved. However, the pinkies which tend to get straight especially for fast runs. I need to train it that the pinkies remain curved as it is a sign of tension, so not relaxed enough. Also for fast arpeggios the other fingers tend to get straight. My worst problem is probably that I tend to play a piece complete with lots of errors and try to reduce the errors little by little with time. So the muscle memory (and ear!) is already used to the ever appearing error. Better seems to immediately eliminate an error as soon as it appears, and not come to a stadium with a big pile of errors what needs to be cleared up. It takes sooooo long this way. So same problem like Pianolady, I need more concentrated and disciplined practise too. In fact, I almost don't make a difference between practising and playing, it is all the time playing with occassional removal of stone old mistakes...
my problem is that I am not following all the fingerings on the score, sometimes I short cut too much. For example, using 2 fingers instead of three fingers on repeated notes. I tend to play the music too fast and should focus on my articulation and phasing... Fater does not mean better.
My concern is trying to play everything with fingers #1,2, &3 and leaving out the 4th and 5th finger.