This is one of those yogi-in-a-pretzel poses that some might find difficult: those with tight hips, tight psoas, knee issues or shoulder issues. So why do it? Cow Face stretches the hips, thighs, ankles, chest, triceps... just about everything!
For ease in the lower body try sitting on a folded blanket and then crossing legs with ankles tucked to the sides. Be sure knees are stacked. If there is strain on the knees, do this pose reclined, crossing the knees and holding at the ankles. You can always practice the arms separate.
For the arms, use the option of holding a strap between the hands, behind the back, one elbow lifting as the other descends, your hands walking toward each other on the strap. I like to give my lower arm and assist by reaching behind my back, grasping my wrist, helping my hand to reach up my back, then reach up with the opposite arm. Another alternative arm placement that I love is arms in eagle arms, with one wrapped over the other, palms touching. This opens up more the back and shoulder blades instead of the chest. Or simply focus on the lower body, bringing the hands to each ankle.
In any of these positions you can increase the stretch by folding forward in the pose. Don't forget to breathe!