I have had a mild case of TMJ before.
Honestly, your best bet is massage. Head, neck, shoulders, and the jaw itself. I had physical therapy when I had the TMJ. Surprisingly, after she massaged my neck (which is always extremely tight), all of the muscles relaxed enough that it wasn't making my jaw pop so much.
Also, physical therapy will give you mouth exercises you can use to strengthen the muscles in your jaw.
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