Without images, all we can do is repeat what you may already have read in your manual or online.
There are a lot of things that cause an image to come out soft. Missed focus is just one reason (and there are ways to verify if that's the case.)
But you can't be a semi-pro photographer and not be capable of focusing the camera accurately. That's a notch away from being a film photographer and understanding everything about photography... except load film. It's sort of pre-requesiste step to being able to do everything else.
Your camera may be in the wrong focus mode. Your camera may have been moving. Your camera may have focused on something other than what you think it focused on. The camera and lens may be out of calibration at the auto-focus sensors (again... there's a test for this.)
There may be a pattern as to what's "in focus" vs. "out of focus". Are you having focus problems only when using low focal ratios? Only when hand-holding? Only when at low shutter speeds? Only with some lenses? Only when using specific focus points (or are you allowing the camera to auto-select the focus point?) Only in poor lighting? The list goes on.
Ultimately, and before you go too far, we should do some testing just to make sure the problem really is you and not your equipment (because it's entirely possible that it is the equipment).
I'd suggest you follow this link:
Jeffrey Friedl's Blog » Jeffrey?s Autofocus Test Chart
That's a downloadable focus test chart (he actually has an assortment of them with the contrast varying). He wants to print the chart on your printer, lay it at an angle (as seen in the photo on his website). You will put the camera on a SOLID tripod. Follow his instructions and take some photos of the test chart after carefully focusing on the center line. When I do this, I deliberately de-focus the camera between each shot in order to force the camera to re-focus. Incidentally... I de-focus a half-dozen or so shots so that the camera is starting at minimum focus... and then another half-dozen or so shots at maximum focus. I carefully record the image numbers so that I know where the camera started. You can sometimes find a pattern where the camera nails focus coming from one direction... but misses focus if it is coming from the other direction.
The goal is to determine if your camera and lens can repeatedly focus on the intended focus point on the chart. Since the chart has a lower-contrast scale printed on it, it is possible to inspect the results to determine if the camera is consistently focusing closer than the intended point... or farther than the intended point. Many cameras mid-range and above cameras allow you to tune the auto-focus system (entry-level cameras typically don't have this feature.)
There are many factors that can throw off focus and in order to improve your focus, we need to isolate all the potential causes of missed focus so we can figure out WHICH of these areas is to blame before we can help you fix it. E.g. giving you advice on how to grip the camera, have a proper stance to put your center of gravity over your feet, support the camera body from below, etc. won't do any good if we find out, for example, that you were letting your camera auto-pick the AF point and there was a closer subject than the intended subjects (the AF systems are programmed to use the AF point that can achieve focus with the minimum focus distance -- it's not random.)
Please post examples.
Include all the settings used (AF mode, AF point selection, ISO, shutter, aperture, whether you were hand-holding vs. a tripod, etc.) Some of the needed info will be in your image EXIF data as long as you don't strip it out when posting.
Regards,
Tim