I had that problem for a long time because of grinding and clenching my teeth in my sleep so my dentist made me a mouth guard to wear at night. It helped a lot and I wore it until my wisdom teeth shifted my other teeth and it did not fit anymore. If you have medical coverage I would suggest trying it, if not, try just buying a normal sports guard, it would essentially do the same thing.
As Maggs87 mentioned a mouth guard is the usual first line of treatment. I used one for a while but for me it did the reverse, I continually clenched on it. I have had success with massage therapy but have had it almost disappear now that I have been diagnosed with fibromyalgia and take Lyrica. It and the massages has been fantastic.
I have had TMJ since diagnosed with rheumatoid arthritis in Oct of 09. My dentist made me a special guard for lower teeth I wear every night. It has helped me a great deal. Was expensive but worth every penny.