Ardha masyendrasana ( half kingfisher ) is relatively straight forward and a lovely posture but the full Kingfisher pose is challenging.
Getting into Purna Matsyendrasana
This is my current approach.
We need a high, tight half lotus. I take my right leg back, rotating the femur head as far back as possible in the hip socket, similar to archer pose but without bringing the foot to the ear.
I like to have my heel to the right of my belly button before rotating the femur back around, bringing my knee back to centre and my foot big up above the groin, still keeping the heel close to the belly button.
Let the right leg and knee settle on the mat then, and here's the trick, lift up a little and lower slightly on the right of the right sit bone.
Take the left foot over the knee, the knee will be half way up the foot, you kneed to have it braced enough that it doesn't pop out of the bind later.
Bring the left knee over, now here's another trick, stretch up out of your pelvis, engage uddiyana sucking in your belly, the space made will allow your foot to point upwards allowing your knee to come further over.
At the same time fill the chest on the inhalation as you bring your knee over, almost holding the knee in place with your chest as you reach behind the knee bringing your right shoulder as far to the outside of the knee as possible.
This should enable you to slide your arm down the leg and grab your left foot.
Settle yourself, open up your body to the side, look over your shoulder and reach around behind your back with your left hand and hold your right hip bone.
Now it's just a case of balancing the three opposing forces, your left knee wanting to open to the left, your right arm pushing your knee to the right but bringing but wanting to turn the body to the right and your left arm and hand on your hip turning your body out to the left.
When you get them all balanced and settle the great this really is one of the greatest of postures.
Below is a link to a video I made earlier today that the above description is based upon http://youtu.be/vVSdO1RYMXU