Take note of the dental history. Any orthodontic treatment at an earlier age, any teeth removed, which would change the occlusal bite.
Symmetry of bite at back of teeth and side. Where are the teeth meeting.
The sub-occipital muscles are related to the TMJ, if one area is affected the other will also be protective, hypertonic and have restricted movement, hence it does not like stretch, but would respond to inhibition techniques.
Check the tone of masseter, and medial and lateral pterygoids. these can be massaged from the inside of the mouth.
The balance of the mandible at both TMJ's is the key hence dentists who use mouth splints and are aware of how the jaw can be changed. This maybe essential to help you treat the patient.
Most important what state is the disc of the TMJ in. Is there a click, can the condyle click on and off the disc, does the disc stay pushed out of the joint and not click back. This stage of clicks will tell you about the disc, without this in a reasonable state you will not help the TMJ very much.
The right assessment working through all the related structures will tell you how and where to work.
Strangely if you do use Cranial osteopathy then it would help to understand the way in which the bones fof the area move relate and can be altered, even so a dentist is often useful to speed things up or change long term problems. Hope this helps.