Eka Hasta Bhujasana requires both flexibility and strength, as well as a healthy dose of playfulness and persistence. For most of us, consistent practice of the pose itself, and/or prep poses to cultivate opening and strength will (eventually) take us there. As always, enjoy the ride!
To begin, practice a few round of surya namaskar A (sun salutation A) to warm up the body. Then move on to the hips. One needs a decent level of external hip rotation to work this pose. Start with pigeon and double pigeon, holding each pose a minute or two on each side. Then sit up tall, legs extended out. Pick a leg, bend the knee and either cradle it (inner elbow crease at the sole of the foot and opposite elbow crease at the knee), or forklift it (elbow creases supporting the calf). Work your shin parallel to the floor and bringing the foot in toward you. Take several deep breaths here as you rock the shin gently side to side.
Eventually take the leg away from you out to the side, keeping the knee bent, and try to wrap the knee crease over the shoulder (ideal) or on the upper arm, working the knee back and up. Hug that inner leg in tight once it’s in place. Set your hands slightly in front of your hips and spread your fingers wide. (see modification instructions below for a variation using blocks) Activate both of your legs and on a exhale, as you slightly lean forward, push the ground away from you and lift up. Your upper back will round slightly. Stay connected to your core and keep your extended leg in toward the midline. Breathe and enjoy and don’t forget to repeat on the second side.
MODIFICATION: If you have two blocks handy, place those under your palms instead of palms on the ground. The extra height that the blocks will give you will make this asana more accessible.