From your first class to your 100th, Downward Facing Dog  is probably the pose you do most often. That's why it's important to do the pose correctly: not only to avoid injury, but also to make it as comfortable and effective as possible. Here are four don'ts when it comes to Down Dogging.
It doesn't look like it, but this pose is all about upper-body strength. If your arms and shoulders are weak, you might compensate by scrunching your shoulders up to your ears. This is a big no-no, as it can cause neck strain, shoulder pain, and headaches. Be sure to actively draw your shoulder blades down your back, creating space in your neck. If you find your shoulders tensing up, it probably means you need to take a break. Bend your knees, rest in Child's Pose, and rise back into Down Dog when you're ready. As you continue your practice, upper-body strength will quickly increase, making it easier to hold Down Dog with correct technique.
A good amount of your bodyweight is in your hands, so be sure this base is strong and stable. Don't allow your palms to lift up; spread your fingers as wide as you can, creating a straight line between the elbows, forearms, and middle fingers. Actively press your fingertips and the knuckles at the base of your fingers firmly into the mat along with the heel of your palm, which can often relieve wrist pain . Your hands should be strong and solid enough that you could jump into a handstand at a moment's notice.
Rounding Your Spine
If your hamstrings are extremely tight and you struggle to straighten them, you'll compensate by rounding your spine. The best thing to do is bend your knees softly , so you can concentrate on lengthening your pelvis away from your shoulders. Don't tuck your tailbone in, but rather stick it out, as if you were pressing your belly button toward your thighs. As your hips and hamstrings open up, you can work on straightening the legs — just be sure your back stays long and straight.
Heels Pointed In
Touching your heels to the mat isn't necessary, as it depends on the flexibility of the backs of the legs. But in order to effectively work your inner thighs, hamstrings, and calves in this pose, press your heels out slightly, so the outside edges of your feet are parallel with the outside edges of your mat. Doing Down Dog this way is more challenging on your leg muscles, but with practice, it'll increase flexibility, and you'll be closer to pressing your heels to the floor.