Downward-Facing Dog seems to be one of the most commonly known and portrayed yoga poses. Maybe it's the funny name - but the Sex in the City girls would often go into this position. It is more properly known as Adho Mukha Svanasana.
If you're female, it's good to have a relatively tight fitting top on for this pose, so that it does not fall down around your shoulders as you press yourself up.
Start by standing with your feet slightly apart, facing down the mat with your feet at one end. Lower yourself onto your knees, and put your hands down on the mat in front of you.
Curl your toes so they become ready to go flat-footed, and position your hips over your knees. Put your arms under your shoulders for stability.
Slowly begin to press yourself upwards. Lift your tailbone up towards the ceiling. Stretch your legs upwards as you go, and stretch your arms upwards as well. Splay your fingers out to give you solid support. Let your head align in between your arms.
As you lift yourself up higher, allow your back muscles to press upwards along with the rest of you.
Press your feet down into the floor, and press your fingers down into the floor, to add to the stability and stretch.
Hold this position for a few minutes, based on your strength and time table. The gently flower yourself back down to your hands and knees and relax.
This is often done on its own as a upper body stretch, but it is also a classic part of the Sun Salutation sequence.
It's important to note that this position puts a lot of stress on the wrists. If you are having wrist problems or carpal tunnel syndrome, it would be best to avoid this pose until you are able to strengthen them.