There is no perfect way to do snake creeps down, only the way you do it now and refining it. But while you’re trying to figure it out think about this.
To get your snake creeps down to work, you should practice standing in horse stance more often and while doing that you should do silk reeling, the kind George Xu (see susanamatthews.com) does or even Zhu Tian Cai‘s. You can see them on youtube. Check out Texas Tai Chi’s Ray Abeyta, too. He has a video on Zhu’s chanshijin style.
While in horse stance shift your weight from side to side while silk reeling: spiraling through bone, ligament, tendon. From the inside outward. The heart cavity should be open. Don’t let the right hand cross past the middle line over to the left side and vice versa. Shoulder joint should be open, as should all joints, but you have to start somewhere focusing your attention. Most people are too tight in the shoulders and if you free them up you are on your way to having an easier time opening the other joints.
It’s true that you refine from where you start each time you begin your daily taiji practice. Perhaps no one can say what “perfect” is, but you will always be better with practice whoever you are.
If you don’t know the finer subtleties of foundational stretches, look for someone who does. Master George Xu can and will show you. Most people can’t bend over much less stretch their legs out wide and down low and graceful as snake creeps down.
To let myself go to accomplish a big stretch like the snake requires is one of the hardest things I’ve done and it’s also one of the easiest. It’s a challenge to overcome. It’s an opportunity to overcome obstacles.Yet buried deep inside is a sense that we all know we are capable of much more. We are created to transcend barriers.