One of the best ways to achieve proper alignment in yoga is through the use of props. Straps, blocks, blankets, bolsters, foam rollers, and even special yoga strap walls are used in many yoga classes to achieve perfect alignment and/or modify the poses. In the following video, I demonstrate how props can be used to achieve Eka Pada Rajkapotasana-aka One-Legged King Pigeon Pose, or just pigeon pose. Pigeon pose requires a lot of flexibility in the legs (it's a prep pose for Hanumanasana, the yoga split) and proper alignment in the upper body. Using a folded blanket, 2 blocks, and a strap, I demonstrate how to modify the pose to get the proper alignment. Unfortunately there is no substitute for flexibility though, so if you don't feel ready to do the pose, wait until you do. If you are almost there but not quite, adding extra blankets for height under the hip and knee should help you get deeper into the pose.
As always, only do this pose once you're properly warmed up. A few rounds of sun salutations after a basic warmup, followed by leg stretches should help. The best leg prep for pigeon pose in my opinion is "rocking the baby pose." To do this, sit with the legs straight out in front of you, then lift the right leg, holding onto the foot with the right hand and the knee with the left hand. Then rock it from side to side as if you were rocking a baby, then switch sides. This will stretch the piriformis muscle that gets worked in pigeon pose.