There are at least two variations on one-leg crow (eka pada bakasana), but this is a good starter variation because it gives the “unused” leg a little more support, and doesn’t require as much back strength as sending the leg straight out behind. Because it gets you comfortable having one leg for support instead of two, it is a good prep pose for more challenging variations. Before exploring one one-leg crow, get comfortable with crow pose: make sure you can hold it for at least 8 breaths (which means you have to actually breathe as you hold it!)
Here we go: begin in crow. Make sure the abdominals are contracted, rounding the low back. Keep the gaze slightly forward on the floor to keep from toppling forward. Squeeze the heels up toward the buttocks. Breathe.
Normally in crow pose, you’d keep the hips up high, but in preparation for bringing the leg forward, exhale and lower the hips slightly. This will allow you to counter-balance better. Keep the abdominal muscles contracted.
Now, shift your weight into the leg that’s going to stay in the crow position. Use the inner thigh muscles to squeeze the inner knee into the triceps (muscles in the back of the upper arm). Feel the other leg get a little lighter. Contract the lower back muscles, outer hip muscles, and buttocks and, and on an inhale, begin to slowly pivot this other leg around and forward. Try not to let the foot touch down. Keep the knee resting against the triceps as a pivot, and squeeze the inner thighs toward each other for more support.
Keep breathing. Keep moving slowly: transitioning too quickly will throw you off balance. Use the chest and upper back muscles to squeeze the arms in toward each other. If the elbows bow out to the sides, you lose your base. As the leg comes around out front, contract the low abs, hip flexors (muscles in the front of the hips), and quads (muscles in the front of the thighs) to extend the leg forward. Breathe.
If you want a challenge, reverse the transition and return to crow, making sure to contract the core muscles and keep the breath flowing. From there, you can transition straight into the other side. Otherwise, from one-leg crow, you can let the feet float to the ground and take a break before returning to crow to do the other side.