You might get better use out of compressing the guitar bus, as a whole, rather than the one individual guitar in the mix. But, I have no idea what your session sounds like or what you're going for. Also, distorted guitars are pretty squashed to hell to begin with. Look at the waveform of the thing and see for yourself.
If you do decide to use comp, you might try somewhere around 2-3db reduction, just in general terms. It may need none, it may help to have a few db's off, or it may help to be massively flattened, depending on the song and the guitar's purpose. In most cases, though, it really isn't needed.