How to do it:
From tabletop pose, with your knees under your hips and your hands underneath your shoulders, place the palms in front of you. Stay here for a few breaths; make sure your back is parallel to the floor. Start by curling your toes under and then slowly move your hands forward, stretching your arms out in front of you and bring your entire upper body down to the floor, while your hips and your knees stay firm, with your buttocks up.
On your next exhale, rest your forehead on the floor, raising your lower back upwards, feeling the stretch in your arms and shoulders.
Rest your head on the floor and with every exhale, take your chest closer to the floor, pushing your arms and shoulders down and forward. Try pushing your tailbone upwards.
You can stay here or walk your hands over to the right, to feel a stretch in the left side of your body. After a few breaths, do the same thing on the other side. Walk your hands over to the left to feel a stretch in the right side of your body.
Come on back to the center now and slide your left arm under your right shoulder for a shoulder stretch on the left. Take a couple of breaths and do the other side as well to get a shoulder stretch on the right. Come on back to the centre, for a traditional Puppy pose.
Stay in this pose for a few breaths, go a little deeper and with your next inhale, raise your head and place your chin on the floor.
Stay here for a few breaths, pushing your heart even deeper down to the floor, while your tailbone is upwards.
When you get out of this pose, on your next exhale, slowly walk your hands backwards.
Until you’re back to sit in thunderbolt pose relaxing your shoulders and your arms, placing your hands, with the palms up or down, on your thighs in front of you.
Benefits of Puppy pose:
Puppy pose gives an excellent stretch to your hips and your hamstrings. This stretch will make your muscles strong, and this will provide your body support.
Great stretch to your entire spine, while relaxing at the same time.
This pose is a restorative pose. It is healing for your hips and your entire back.
Puppy pose is a great way to relax your shoulders and your arms while giving them a stretch.  Your lower abdomen gets activated while trying to take your hips upwards, making it a great core workout.
When you move your lower body upwards and the upper body downwards, breathing slow and deep soothes your muscles around your entire spine and your hips, which will calm your mind and your body.
In this pose, your chest will open, this will reduce the tightness around your back and shoulders. The opening of your chest will improve your breathing and the capacity of your lungs. Since puppy pose is an inversion pose, it is very beneficial for your blood circulations.
The deep stretch in your shoulders and chest with the flow of your blood going towards the opposite direction can act as very calming and stress relieving, very beneficial for insomnia.
Contradictions:
Avoid this posture if you have any knee or hip injury.
Always get out of this pose if you feel any pain or discomfort.
Modifications:
Try putting a blanket or a pillow under your knee and underneath your chest. This will relax your body completely.
If you support your arms and your head with blankets or yoga blocks, you will reduce the unwanted stretch at your neck.
The longer you stay in this pose, the greater the benefits.