Surya Namaskar or "Salute to the Sun", as with other forms of exercises, can be done whenever your stomach is empty. However, the most appropriate time to do Surya Namaskar is when the Sun is just at the point of rising above the horizon, that is, early morning; but it is not a "must". Every time that you perform this exercise you should face the Sun. 

It is best to do this exercise with all the windows of your room open, or in the garden on the lawn under the open sky. You should have as little clothing on as possible, or wear light clothing in which you can move about freely, when doing this exercise. It should be done with bare feet. 

There are 12 positions in Surya Namaskar. 
 
In the first position, you stand erect, alert but not tense, looking straight ahead of you with the palms of the hands joined together at chest, your feet closed in, toe to toe and heel to heel. Think of the sun as the eternal source of light and power. Breathe in and, then out as you extend your arms in front of you at shoulder level, palms 
down. 

It seems to be the case that many people have forgotten how to properly breathe. They pull in their stomachs when they inhale and push out their stomachs while they exhale. This method of breathing is incorrect. The correct way is to push out or distend your stomach as you breathe in, and to pull in or contract your stomach when you breathe out. In this way, you can inhale more deeply, as well as exhale more fully. Thus, in the first position when you are inhaling, you should throw out your stomach or distend it to the fullest extent; then pull in or contract the stomach as you exhale. This also exercises your kidneys and liver, every time you inhale and exhale. 

In the second position, you raise your arms high over the head and bend backward from the waist while deeply breathing in. 

In the third position, you breathe out while bending your body forward, so that your hands go down as far as they can. Do not strain yourself. Your head should eventually come in contact withyour knees. The legs should remain straight. 

In the fourth position, you move your right leg backwards while keeping the left leg where it is. Here the left leg, which must be kept stationary, is bent at the knee and the knee of the right leg, which is to be moved backwards, should be resting on the ground. The right leg touches the ground only with the toes and the knee. Relax and move your body forward a little. Raise up your chin and chest while inhaling deeply, distending your stomach to the fullest. By doing this, the heels of your hands are automatically raised up, only the tips of your fingers still rest on the ground. If this position is properly done, it tones up your liver and kidneys, and exerts gentle pressure on your abdomen, helping proper elimination. 

The fifth position is assumed when you throw your left leg back, to the full length of the leg and, then, throw the right leg back, as well, making a plank; the head, back and legs form a straight line. At this point you should hold the breath. 

In the sixth position, you bend the arms and let your body come to rest on the ground with the eight points, or astanga, of your body touching the ground. These eight points are: the two feet (toes), the two knees, the chest, the forehead and the two hands (palms). As you lower your body down, exhale as deeply as possible, expelling all the air out of your lungs; at the same time, pull in the stomach. 
 

In the seventh position, you raise your head and chest upward, the full length of your arms; bend backward and raise your chin up as high as possible. Breathe in. 

In the eighth position, without moving the feet or hands, you raise up the entire body so that your bottom is in the superior position, like a mountain, with the knees and elbows straight. Try to touch the heels and the top of the head to the ground. Breathe out. 

The ninth position is achieved by dropping the left knee down on the ground, about half way between the hands and the feet and, then, bringing the right leg forward all the way to the hands (in reverse of position No. 4). Breathe in. 

The tenth position is achieved when you bring the left leg forward, putting the left foot at the side of the right foot; letting the hands remain on the ground in order to repeat position No. 3. Breathe out. 

In the eleventh position, you return to position No. 2. Breathe in. 

In the twelfth position, you lower your arms down at your sides. Breathe out. 

These twelve positions make one round. It is essential to point out that you should perform Surya Namaskar twelve rounds at a time. If you are tired on any round of the exercise, you can rest and, then, resume again, until twelve rounds are completed. 

Surya Namaskar is never complete without proper breathing. Breathing is the rhythm, the rhyme and the life of this exercise. You must, therefore, be very careful to do this exercise properly, in order to master the technique of breathing. Without proper breathing, this exercise is just an exertion. With breathing properly done, it charges your personality with unbounded cosmic energy.