There is no such thing as an overwound clock. This is an "old wive's tale" If your clock is fully wound and wont run, there is some other problem. It is impossible to over wind a clock (unless you turn the key so hard you bust a spring). If the spring is broken, the key will keep turning and never tighten up. If your clock was running and just stopped working, it may just be out of beat or need cleaning.

If your clock has a pendulum, it must be level in order to run. If you have a balance wheel movement it won't make any difference.

Don't move your clock with the pendulum attached. Doing so can knock it out of beat. If it's pushed up near a wall and not possible to remove the pendulum first, you can cheat by tipping the clock toward you while moving it a short distance. The pendulums on some clocks, such as Vienna Regulator can be tricky to remove without damaging the suspension spring. If you have this type of clock you can use some low-tac painters tape to hold the pendulum bob in place to move the clock for a short distance.

Remove any weights before moving your clock. This should be a no-brainer.

Don't move the hands backward any more than a few minutes. Doing so can damage the movement. To set the time, move the hands in a clockwise motion only, stopping to let the chimes cycle. If the chimes are out of sequence, simply move the hour hand to match the chimes, then set the time as mentioned above. 

Have your clocks cleaned and serviced on a regular basis. Every few years is recommended. The last service date is usually written on the back door of the clock somewhere. If your clock gets dirty and dry, it can wear out the bushings and you will have a much more costly repair on your hands.  

Do not use WD-40 or anything other than clock oil to lubricate your movement. I can't tell you how many clocks we have come across that are saturated with this gunk. It won't help and will make a big mess. Oiling will be taken care of when you have your clock serviced.

Don't throw away any "extra" parts!  If you find an old fixer upper at a flea market or estate sale, be sure to check inside the bottom of the clock case. You will be amazed at what you will find there.

Be wary of a clock repair person who wants to replace your movement with a reproduction or a cheap quartz movement. Some clock movements can be very valuable and though most people are honest there are some unscrupulous people who would tell you your movement is beyond repair so they can keep it.