Start in tadasana/mountain pose. Shoulders should be rolled down the spine, arms in anatomical position (palms forward), quads engaged and weight centered on the foot, evenly distributed from the heel to the ball of the foot, toes spread wide.
As you inhale, raise the arms over your head, looking up but not cranking your neck. Hands should rotate inward so that the arms are internally rotated from the shoulder.
As you exhale, fold over at the hips. Your hands come by your feet and your neck is relaxed. Make sure to keep your weight shifted forward so that you get the most out of the stretch - the tendency is to shift the weight back to balance the weight of your head coming down. But that takes away from the awesome deep stretch of the forward fold! So keep your weight forward. Don't worry, you won't fall. At least, you probably won't :)
On your exhale, fold back over.
Up next is the chatturanga. Check out this post I did a few weeks back that goes into detail on the proper way to execute that challenging series of poses. For Sun Salutation A, you can either jump back, landing in chatturagna (super advanced) or you can walk your feet back and go from high push-up/plank pose, shifting your weight forward and then lowering into your chatturanga push-up.
|Lower into chatturanga|
Now you transition back into downward facing dog. If you're more advanced, you roll over your toes by pulling up with your core and pushing away with your arms. If you're not quite there yet, pull up with your core while you push back with your arms and simply move the feet so the bottoms of the feet are on the floor.
Now to start the Sun Salutation A sequence over again, either jump or walk to the top of your mat, and start back over at the beginning. This is a very popular sequence to warm the body up in a yoga class, typically being done within the first 10 minutes of a class.
Now you can be a Surya Namaskara A pro, getting your body warmed up and ready to flow your way through the rest of your class!