Some of the yoga poses listed below should help with some muscle relief. Some may seem to be more shoulder-muscle related but should help to relax the neck and jaw muscles.
When you start to feel the muscle tension begin, take a deep breath in, then as you exhale, relax your shoulders, as if someone is trying to press the shoulders down away from the ears. Do this 5 times. If the tension isn't too bad, bring the shoulders up on te inhale, and drop them down on the exhale.
Scalp massage will also help with the jaw. Take 3 extra minutes in the shower to massage the scalp all over.
Eagle Arms - find a comfortable seated position (on the floor or a wooden chair). Breathe in and reach your arms to the sky. As you exhale, bring your arms down and wrap your right arm under the left like you're twist-tying your forearms at elbows and wrists. Lift the elbows so they're at the same height as the shoulders and take your thumbs further away from the face. Stay here for 5 breaths. Repeat on the other side. *there are a number of YouTube videos that can guide you through this as well if a visual aid is more helpful
Camel Pose - stand tall on your knees. (Ears, shoulders, hips and knees are stacked in one tall line). Place the palms of your hands on your low back (a little higher than where jean pockets are). Relax the shoulder. Squeeze the elbows close together. Slowly bring your gaze up until you feel a long stretch in the front of the neck and chest. Keep your teeth together but not clenched. Stay here for 5 long breaths. Big inhales will help you feel the stretch.
Head tilt - find a comfortable seated position. Reach your right arm away from you (if you're on the floor, with your right fingertips on the floor, walk the fingers away from the body). Drop your left ear to your left shoulder. Stay here for 5 breaths. Repeat on other side. Once the muscles warm up, between sets, alternate dropping the chin to the chest and lifting the chin to the sky. When lifting the chin, keep your teeth together but not clenched.
Downward dog - start on all fours with your hands on the floor under the shoulders and the knees on the floor under your hips. Curl your toes under, lift your knees off the ground and lift your hips up. Bend your knees as much as you need. Try and relax the shoulders. Press the hands into the floor to bring your chest closer to your thighs. Relax your head. Shake it yes and no. Separate the teeth relax the jaw.