Adho Mukha Svanasana is one of the most common poses in yoga and great for building upper body strength, stamina and stretching the entire body.
No matter how I feel, I always manage a Downward Facing Dog! I honestly can't remember a day where I haven't practised at least one. Being able to carry part of my own body weight on my arms makes me feel strong and able.
For beginners, being able to hold Down Dog pose comfortably really shifts your practice. It indicates a certain strength and ability to perform the pose correctly. For some extra tuition in Downward Facing Dog Pose why not have a quick look at this short tutorial -
Straight spine v. straight legs
To enjoy Downward Facing Dog and begin to feel the bliss that being in this pose can potentially bring you, you need to be able to shift most weight back towards your hips. If all the body weight falls forward in the arms and the upper back rounds, it will not feel stable or enjoyable.
If the hamstrings and/or lower back are tight, this can result in a rounded spine. If that's the case with you, try bending the knees and lengthening your spine, shifting the weight back towards the hips. Simultaneously, press into your hands and extend the arms. Drawing your belly in also helps to take the weight back. You will suddenly feel much lighter and happier in the pose.
Don't be too ambitious about straightening your legs and pushing the heels to the floor - you might need to be in Down Dog with the knees bent for a while! Only when you can keep the spine long while extending the heels down, can you then start straightening the legs.
Here's a step-by-step description of Downward Facing Dog pose.