There are lots of reasons you could be having soft pictures. Some of them...
1) focus not at right place due to operator error (wrong point focused on)
2) focus not at right place due to camera making the focusing decision (camera was allowed to pick the focus location, and picked wrong)
3) focus not at right place due to either front or back-focusing by camera (needs repair center adjustment)
4) Sharpness of focus not achievable with lens (soft lens or poor copy of lens)
5) camera shake (too slow a shutter speed)
6) motion blur (too slow a shutter speed)
7) DOF too thin to allow all areas of interest to be in focus (aperture too wide)...
I'm sure there are other reasons/causes, but to figure out what the problem is, you need to tackle each possible cause on its own. For instance, to eliminate camera shake, put the camera on a tripod for test purposes, use a remote trigger, and perhaps even use flash. To achieve critical focus, use the live-view function on a clearly defined target with lots of detail, using manual focusing. If this gives you good sharpness, then you know it's not the lens. Next, set the lens from manual focus to autofocus, select the center point, and let it focus on the same target you shot earlier. If the camera's autofocus is working well, you should have exactly the same point in focus. If not, then the camera is either front- or back-focusing. If this test passes, then switch the focus selection points to auto and see what it focuses on. Chances are the camera will focus on the brightest or highest contrast or the closest point, which may or may not be the point you wanted the focus on.
By approaching this systematically, you can figure out where the problem is, and address it.
However, I still can't see any details. You could at least provide us a little bit more info while you're figuring out the forum 
