I don't know if I've already posted this, but my method is a variation of Ross's method, but it is foolproof(*).
1. Chill the kegged beer to serving temperature.
2. Attach gas hose and set reg to desired carbonation level (14-6psi almost always for me, which is also my serving pressure).
3. Rock the keg until the regulator stops hissing.
4. Rest the keg for an hour or so (optional).
5. Serve.
This method always(*) works. As the reg is set at the desired pressure, you cannot overgas. As long as your rocking exposes more surface area of the liquid, gas will continue to go into the beer, so if you hear the hiss, rock some more.
When I set up my kegs, I wanted the least fuss possible. ie, one pressure for both carbonating and serving and it turns out this is right for force carbing as well. It may take a little longer than starting at a high pressure and turning back when it's close to carbonated, but you cannot(*) overcarbonate using this method.
(*)-No guarantee in contiguous states of Australia, nor Tasmania, nor any territory or protectorate of Australia, or any country on the same planet.