I have the same problem, although it's slowly starting to go away. I've taken all the measures that have been recommended here, but it's still something I struggle with. From what I can see it's just a matter of practice. The more trigger time I get the better I become. I'm still throwing a bunch of shots low and left, but it's happening much less frequently now.
I also think part of it is patience and mental discipline. I can usually tell when my shot is off, and more often than not it's because I jerked the trigger. But if I take my time and really concentrate I can (for the most part) hit what I'm aiming at.
I know what I have to do. Control my breathing, line up the sights, and slowly and steadily squeeze the trigger. Much easier said than done though. But it'll come with time and practice.
Don't stress out too much. Shooting is supposed to be fun.
BTW what are you shooting?