I have the same problem, my arms just kind of shake I guess is the best way to put it. I don't have any kind of diseases or disorders, nor do I have a flinch; my hands just aren't very steady. I also shoot fine with rifles.
Its like they say though, practice makes perfect. I go the range whenever money allows, and do tons of dry fire practice. The dry firing has really helped.
While I am by no means an extremely accurate shooter, all the dry firing has helped considerably and my groups are getting smaller.