This is a cracker of a topic. If you can't take sharp pictures you are not going to enjoy your photography. It is perfectly possible to intend to take a blurred image (for the artistic among us) but that is more subjective and much more difficult to get a predictable result.
So for the sharp minded (pun intended) you need to pay attention to three things:
1. Your eyes; we're not all perfect so get regular eye exams and follow the usual advice. Don't look at the sun, don't look at arc welders, don't run with scissors....
2. Your camera. If it's broken get it fixed. Autofocus systems are complex and don't react well to sudden falls (actually it's hitting the ground that is the main problem). Pointing your camera at the sun for a sunset shot can damage the autofocus sensor(s). If your using manual focus (by necessity or if your a control freak (you know who you are)) then accurate focusing technique is important. Practice, practice, practice.
3. Your camera. No, it's not a mistake, it's a different type of issue. Shutter speed this time. It may seem obvious but in some ways it isn't. A good photographer can take a sharp image at 1/50th of a second. I know of exceptional people who can do it down to 1/20th of a second (and one guy, quite famous, reckons he can do it to 1/10th of a second but I seriously doubt it reproducible in more than 10% of attempts).
Back to 1/50th of a second thing - This is true but only for short focal length lenses. The longer the focal length, and the more magnification you are getting, the more effect camera shake will have on the image. The guide you should use is to use the [35mm equivalent] focal length as the minimum shutter speed you will get a good result from. So a 200mm lens should cause you to use 1/200th of a second shutter as a minimum (faster will be less prone to blurred results).
This brings into play an interesting divergence. The longer the lens the harder it is to isolate the subject, to be sharp, from the background (if it is moving). There is no real answer to that unless you use post capture editing with a computer and a measure of skill.
Hope to see you again soon. Send in your comments! Requests by, well, request.