My secrets about marichyasna C for Quentin, this passionate Ashtanga bone:
First sit correctly. The outer side of the foot is in line with the outer side of the body (and not next to the stretched leg!) This might make the pose more challenging, but so it is. Sit upright. Feel your hips and sit erected. Lengthen the body when inhaling, this creates room.
I usually lean a bit backwards and then I shift my weight forward and diagonal, to bring my shoulder far in front of the knee. I push the knee to the other side. This happens with an exhaling, but before exhaling it's important to engage the bandhas (mula bandha and the adbomen). This creates room and every inch counts. The movement starts from the hips, the spine turns. All movements start from the core of the body. The breath initiates each movement. When the shoulder is placed firmly in front of the knee, wrap the bended leg with the arm. The weight is still more on the right side.
When the arm is behind the back, bring the other arm to the back, too. It's better to think of the shoulder and to move the shoulder backwards. If you don't do this you lose inches that you might need. It's not about holding the wrist. This pose is a twist, one shoulder moves forward, the other backward (always shoulders move down, away from the ears). The chest opens. The trick here is to bind rather high on the back as this is the shortest way to get together. When the fingers are hooked or when you hold the wrist, you can stretch the arms till the one hand can lie on the stretched upper leg. Now the weight moves to the middle again. M uses to say: press the knee against the arm. This supports the twist.
Bringing the shoulders down helps to reach the leg. The stretched leg is engaged, the foot parallel to the wall. With each inhaling I stretch the body, with each exhaling I go deeper into the pose, means I twist more. Breathing is important. In the beginning there seems to be pressure on the chest that scarcely allows to breathe. Nevertheless breathe. Deep inhaling.
All twist poses seem to be easier when the body is slim.
All twist poses are more challenging with relative short arms. Who cares.
Twists neutralize poses, it is said.
Dristhi is not the nose, but the side. This helps to keep the body upright.
Currently I'm working on doing the above described movements within one exhaling. I'm still a bit too slowly. Sometimes I need one extra breath. The vinyasa count is important, too.
PS: The head turns last. It's moving the chin to the side. Check on pictures your head falls aside.
Good luck. Let me know if it worked.
Feed-back in form of comments is welcomed.