So, I exaggerated very slightly - the best way to do these exercises is with a combination of eye and jaw motion. (You can do it with just your eyes, but it tends to take a little bit longer.) These three exercises can be done independently, or one after another in any order.
The reason it works is because the jaw is an absolute mess of muscles. But, it means that a little work anywhere ends up helping problems everywhere.*
Exercise 1: Eye motion for jaw tension
Lie on your back, or sit in comfortable upright posture
Set your jaw into a neutral position. (You can move it around later)
Slowly scan your eyes side/side across your field of vision, and then up/down. Keep your eyes shut while you do this, and try to keep the motions small and smooth.
This should literally be as slowly and smoothly as possible. It even works if you basically just imagine that your eyes are moving. Later on, you can build on this and move further. Your eyes will feel weird and jerky and that's fine. They always are, you're just going to notice it. If you do this a lot, they'll get smoother.
Take 3 paths side/side and 3 up/down. You're going slow, so this should take at least a minute.
When you finish, move your jaw to another position. I like to try closed (use your hands, so you do not clench while you're doing this), neutral, and open.
Exercise 2: Jaw motion for eye tension
Move your eyes as far as they'll go in a direction (you'll go in others soon enough). If you have jaw tension, you're going to quickly hit a point where you feel pain behind your eyes, and also probably some pain deep in the back of your jaw.
Move your eyes into the point where it is uncomfortable, but not painful.
Holding your eyes at that spot, slowly (literally as slow as you can) move your jaw side/side, front/back, and open/closed. These motions should be extremely small and very slow. You can also, again very slowly, move your jaw all the way open and all the way closed.
As you do this, your eye muscles will start to relax, so keep reminding yourself to sit at that point of discomfort (but not pain, never pain).
At some point, you're going to realize your eyes don't really hurt in that direction anymore, so start looking in a different direction. I like to move around 8 compass points.
You can also do the jaw exercises without the eye positioning.
Exercise 3: Jaw and eye motion for jaw and eye tension
This is a combo of the two above techniques
Move your jaw side/side or up/down while your eyes do the same thing.
Move your eyes up/down while your jaw goes up/down, then do a set where your eyes go down/up while your jaw goes up/down.
For bonus points, try to have your eyes go up/down and your jaw go side/side. You will end up clenching your jaw with the focus, so don't do that. If you notice the tension, set your jaw neutral and eyes centered.
You can also do tiny movements, again. Doesn't have to be big.
Your eyes and face will feel kind of droopy after this, and your eyeballs will feel sort of weird with how easily they can move.
These are based on Feldenkrais exercises, which are about slow, small movements to build neural pathways. They're boring as shit because you feel like you're not doing anything, and then you realize that it's helped a lot.
These exercises should be very small I know I emphasized this a lot) because the point is to build healthier movement pathways, not to stretch or exercise. If, at any point, you feel your jaw starting to tense, stop the exercise you're doing and reset to a neutral jaw position and go again. Again, the point is practicing not having jaw/eye tension, so you completely miss the point if you tense up and allow yourself to stay tensed.
Bonus exercise: jaw tension resetting exercise
This one is to train the pathways that help your jaw relax, so you can get better at it. You're going to tense slightly and then practice undoing that.
You're welcome to use your hands here to help guide your jaw into a relaxed position, or super gentle pressure on the tension points. But, this is not a massage. You are using the fingers to help focus the relaxation or to guide your jaw, but the point of this is that your jaw is learning to relax itself.
Tense your jaw slightly. For most of us, that's going to be "stop trying to relax your jaw" and it'll go somewhere tense.
Consciously try to relax. Give it a couple seconds. You do not have to relax fully, and you don't have to do it completely. Even letting go of a little tension is good.
Let your jaw go back into whatever natural tension it has, but see if you can keep this from going to full tension. Consciously relax it over a couple seconds.
Try to do this at least 10 times. Over the course of these exercises, you're going to end up relaxing other spots in your jaw than you originally felt.
This sort of exercise can be used to help train you into not hunching as well. Slowly training the reflex to get back into good posture every time you lose it.
* Fuck, you can help jaw pain by rolling a golf or lacrosse ball underneath your foot at the pressure points. The relaxation runs all the way up your back and onto the back of your head. If you roll the ball under your feet for about 30 seconds each foot and then try for a hamstring stretch, you're going to discover you have like 6" more range of motion without having actually stretched. And on the flip side, rubbing your temples or the muscles over the top of your head can help your hamstring range of motion slightly.