As you might have noticed, this is not the most natural position in the world; every muscle and every bone is being asked to reverse itself and go someplace that, for a few days, it will refuse to go! Men especially have problems because of larger biceps.
Try it this way: first extend your arms to the sides and then swing them together, wrapping the right arm as far around the left as the force of the swing will throw it. You will then find that the best way to work on the palm to palm is to get the pads of your fingertips together by whatever necessary contortion and, using your fingertips as leverage, push them against each other until – eventually – the palms will touch.
Making a proper Eagle’s beak under your nose will be beyond you while you are still wrestling with the wrapping of the arms and the touching of the palms. But even if your hands and arms are not right yet, pull downward with the arms as hard as you can till the arms touch the chest. One of the greatest benefits of this posture is the flexibility and strength developed in the shoulders by this pulling. It also releases all those neck and shoulder tightness’s that give stiff necks and tension headaches.
The trick in getting your toe wrapped around under your calf muscle is an opposite technique to the “swinging” of the arms into place. Bend your legs and get yourself good and set. Then ever so slowly lift your right leg up really high and reach as far left with the whole leg as you can, lowering in on the far side of the left thigh and deliberately wrapping it as far around the left calf as it will go. Use the toes of your right foot, especially the big toe, just like fingers to reach and grasp with, even if you can´t reach your ankle yet.
Some people have so much difficulty with one-legged balance at first that they have to steady themselves against a wall, get the leg wrapped as well as possible, find their balance, and then wrap the arms.
As a general rule, however, is you concentrate on one point in front of your face and then sit down as much as possible and straighten your spine, you’ll find passable balance after a day or two.
Getting the hips square to the mirror and level, striving to sit even more deeply, and creating the “nut-cracking” opposition in the legs are refinements that you will be able to concentrate upon fully only after you’ve found solid balance.
Your initial success at this pose will depend upon the length of your leg from knee to ankle as well as your balance and flexibility. People whose forelegs are shorter must make up for lack of length by gaining even more flexibility than the rest of us.
The Eagle supplies fresh blood to the sexual organs and the kidneys, increasing sexual power and control. It helps firm calves, thighs, hips, abdomen, and upper arms. It also improves the flexibility of the hip, knee, and ankle joints and strengthens the latissimus dorsi, trapezium and deltoid muscles.
Read more about this poses benefits, pictures, video and tips from here
Drawings and info from "Bikram´s Beginning Yoga Class " Book, 1978.