Since you ask a pretty general question I am going to try for a general answer, as this question is asked probably more than any other single question in many forums.
To figure out the issues you must become a bit of a detective. First, gather all the information you can. Among the things you should try to get are:
Lots and lots of samples, as one bad shot is very hard to diagnose in isolation. Then look for patterns in them, among such issues as below.
Failure to acquire focus will usually result in some area of the image being in focus, while desired areas are not. Look close at the background and foreground (grass and other textured surfaces are a good place to look). If you find a specific area in focus (but not the one you want), you can (mostly) eliminate vibration or motion issues.
Look for motion. For subjects, see if stationary subjects (or ones that match your panning) are in focus while others are not. Look for smearing - does the blur you see seem directional - looking at points and lines in different orientation will help you. If you see a consistent smearing in one direction, that is most likely motion of the subject or the camera.
It is worth noting that motion blur can be difficult to see, especially camera shake. It might just appear as a blur. Also do some tests with support - tripod, monopod, bean bag - whatever is appropriate. Take some shots with a timer so your hand is not even involved. See if these result in less blur than your hands.
Carefully looking at the two issues above will usually help distinguish failing to acquire focus from motion blur.
Another cause is equipment vs. expectations. It is always worth getting a perfectly in-focus shot with your equipment so you know what it can do. Cameras with live view are easiest - put it on a tripod, use a zoomed-in live view image to focus very carefully in manual mode for a stationary object, and take a shot. Take a few. You must use live view, never the viewfinder to focus, as live view is the real sensor data. Because this eliminates the auto-focus mechanism all issues of back/front focus and such are eliminated. If the resulting shots are not clear (and you have been careful), suspect your expectations are not aligned with your equipment. Be sure to check multiple lenses, with and without filters (I often see really cheap, poor filters on really nice lenses). Know what your equipment can do, to judge against what it does routinely.
Metering and light can be an issue but would be at the bottom of my list for concerns. Really high ISO shots will be blurred a bit by noise, and conceivably you may be in an area too dark for your AF mechanism to work. But frankly you would likely already know that, the effects are not that subtle. White balance and exposure per se has no real affect on focus.
Post processing can also be an issue. Some people will shoot raw, and then apply no sharpening at all. Most DSLR's need some level of sharpening just to reach "normal". Experiment a bit, if you post process, with sharpening settings, and if not with the in-camera controls. But again, I would put this closer to the last things to worry about.
Now... where you go from here depends on what you find. Probably (sadly) you will find some of all of these issues, since humans are involved as well as imperfect equipment. But gather a lot of data and see which area you most need to work on, then research it, or ask about it, with some specifics. I cannot begin to address each possible cause in one answer as my fingers will wear out.
But... you will be continually frustrated (especially when asking for help) if you just use a shot at a time, as there are so many possibilities. You need to be aggressive at experimentation and collecting samples to see where the patterns are. Since you cannot go back and time and fix any one photo, your goal should be to figure out where your most prevalent problem lies, and fixing it by changing what you do, then move on to the next.
