I have TMJ. If you have it, here's a couple sites that contain a few of the exercises done to account for it:
http://www.nismat.org/ptcor/tmj and some other information about treatment:
http://www.tmjhope.org/10-tmj-tips-physical-therapist/
One thing to remember is that TMJ can come about because of numerous different sources. I spent a lot of time dealing with back and neck issues, not things related specifically to my jaw. I spent time on those things too, but stresses from bad posture can play a large part in TMJ, thus the back and neck attention. (And the chin tuck thing seem stupid, but it does help for some reason. I'd also add stretching your neck muscles, using your left arm, grab the right side of your head, and pull it over some to stretch your neck, hold for 15 seconds, then reverse sides. Another is to grab the back of your head, with your palm over your scalp, and pull you your head down towards your armpit, again hold for 15 seconds and then switch. Also, rub your jaw muscles next to your ears in a downward motion, applying decent pressure, but not hurting yourself.
Also, something I didn't see listed is to keep your tongue planted on the roof of your mouth, and to hold your fingers behind your jaw, keeping a slight forward pressure. Then open your jaw and repeat 20 times.
All the while you're doing this, you should keep good posture. Posture is very important to all of this. And don't sit at your desk for too long without moving.
These should all help.