One simple piece of advice can completely change the experience of the body and set it free from the mind's unintentional tyranny: Don't clench your teeth.
I'm pretty sure that we've all found ourselves clenching our teeth, making a face, or generally feeling tension around the jaw, neck, or collarbone area from time to time during yoga class, especially when attempting a pose that requires the muscles to do work that they might not be completely accustomed to doing.
Even before I really started to pay attention, I could have told you that clenching your teeth or contorting your face doesn't actually help the quality of your asana, but what I didn't completely realize is that unnecessary tension in the face and neck was actually robbing my muscles, not only of their strength, but also of the joy they take in their own work.
When I'm in a pose that is difficult or strenuous and I find my face attempting to assist my legs by scrunching itself into some odd shape, I give my entire head area permission to rest, while the parts of the body that are actually involved in the pose are allowed to do the necessary work on their own. It turns out that those active muscles, the ones that are necessary within the asana, really enjoy being left to their own devices. They instantly respond by exhibiting increased strength and focused proprioception (they know where they are in space), and they even give me direct feedback, letting me know that the work that they are doing is not really "work" at all. It's just muscles doing what muscles do– and they love doing it.
This isn't a big secret. We've all probably heard a teacher's admonition to relax the jaw– and it's awesome advice. It's also much more profound than it might seem, because, of course, relaxing the jaw isn't just relaxing the jaw, it's relaxing the mind, at least relaxing the mind's tendency to butt in where it isn't actually needed. Your leg muscles can really handle Warrior 2 on their own, but the mind is under the delusion that it is the sole arbiter of action within the body and that without it's involvement the body would be a dumb lump of unmoving flesh. This is just a bad habit of thought, though, because when we do give the mind permission to rest, it's like the mind wakes up from a dream and realizes that it really didn't have to be doing that at all. Suddenly the mind is free to do much more interesting things than boss the muscles around, and it quite enjoys its freedom. The mind might check in with the breath, reflect on this new sense of joy, or even just rest for a bit.
When the mind ceases its efforting on behalf of the body, the active muscles become much more stable, more acutely aware of their own role in the situation at hand, and whatever work they are doing becomes much easier, as if they had a reserve of extra energy that was somehow being suppressed by the mind's attempts at control. And when the mind relaxes, the body relaxes too– the face, the jaw, shoulders– they all get freed as the mind frees the active muscles. More strength and more relaxation at the same time. We like that.
The simple practice of noticing tension in the jaw/face/mind and then allowing it to release it can have repercussions that extend way beyond the mat. The other day I was hiking up a steep incline at about 9,000 feet, when I noticed that, unlike in most of my earlier life, my mind, my jaw, and my entire upper body were totally relaxed, breathing, enjoying the scenery, and just sort of riding along on top of my lower body. At the same time, my legs were working super hard, and they were loving it. Far from feeling strained or fatigued, my whole lower body felt energized, powerful, even joyful to be doing what it was doing. I realized that this reminded me of an image I've encounter over and over again: the centaur. I'm a Sagittarius, so I've been familiar with this image for my entire life, but I never quite got it before that day on the mountain. I now see that powerful horse body with the man on top and I know how it feels. Maybe that's also why centaur's are said to be so wise, because their minds aren't caught up in the worthless pursuit of unnecessary effort.
Besides just blaming "the mind" for these strange habits of clenching and tension, there's might be a more specific way of accounting for what's taking place, and it has to do with the sense of "I". When the sense of "I" tries to take control of the leg muscles, "I" am left feeling like "I" have to make the effort, that "I" am responsible for the work the legs are doing.
We all know this feeling, and we have the lines etched into our brows to prove it. But when "I" realizes that the leg muscles can actually take care of their own work by themselves, then not only are the leg muscles free, but so is the sense of "I", and when the sense of "I" gets freed from its unnecessary entanglements, that's when things really begin to get interesting.