Just make sure you are aware of the fact that mixing in mono does feel quite different from stereo. But if you get it sounding good there. It will sound great on your other speakers in stereo.
If you mix rock/metal, try the Cardinal Points Mixing approach where you basically pan every mono source either hard L, hard R or Center. Will translate really well in mono and makes mixes really wide and punchy. Doesn't always work, especially if you have a lot of stereo mics, but I use it very often and like it a lot. For more info go here:
http://recforums.prosoundweb.com/index.php/t/13724/0/