From this position, on forearms and knees, curl your toes under so that the balls of your feet are on the mat and then lift your hips, as if you were going into downward facing dog (adho mukha svanasana). In fact, dolphin can be a useful variation of downward facing dog, if you have sore or injured wrists.
From this position, many use dolphin as a core strengthener by pivoting between the high hip position to forearm plank and back. The distance between your feet and your elbows will depend on the length of your body’s extension in the plank position. You want to be able to come into a straight line from your head, through your shoulders, hips, and legs. This movement is probably how dolphin got its English name, since this replicates how dolphins move in the water. Using dolphin this way strengthens not just the core but shoulders and legs as well.
Scorpion pose (vṛscikasana) is closely related. From peacock pose, the yogi moves into a backbend, eventually placing the soles of their feet on the back of their head. Scorpion is described in the Hatharatnavali (also 17th century).
To use dolphin as a forearm balance preparation pose, walk your feet in toward your elbows as far as you can, lifting your hips and bringing your torso as vertical as possible. From this position, experiment with raising one leg at a time, eventually bringing both legs up. You’ll want to do this at the wall to start, to avoid over-rotating which could lead to neck or back injuries.
Dolphin is a strong pose. Make sure you’ve warmed up adequately before moving into it. And not just your shoulders and back, which are obvious, but your hamstrings and calves which get a mighty stretch here, too.
The benefits of dolphin, besides the strength and the stretch, include all the benefits of inversions. It’s good for your vascular system because it challenges the normal flow of blood against gravity; it helps your immune system by moving the lymphatic fluid along; it benefits your bones by giving your arms some weight-bearing exercise; and it's a mood lifter, because it’s really hard to go upside down and stay depressed or really even serious.
The ancient yogis named poses after animals because they shared their environment. Now days, we can use the animal names and characteristics of poses to remember our connection with Nature and the interconnectedness of all life. And maybe we can use dolphin to emulate the playful, friendly disposition of these beautiful, intelligent, endangered creatures.