Ideally, you should develop your foundation in zhan zhuang (learn how to sit down while standing, get a sense of the feeling of connection, develop a thread to pull) before practicing silk reeling (practicing "pulling" the thread). If you jump into silk reeling exercises before or at the same time that you begin zhan zhuang, be mindful to not get stuck on "this is what silk reeling is" where you were when you learned the exercise. Be open to allowing your silk reeling practice to evolve. I play my silk reeling as a moving zhan zhuang.
So what is "the thread" referred to in silk reeling? My understanding at this point is that "the thread" is something like the attentional/intentional/fascial kinesthetic tactile connection that is felt when you kinesthetically feel it in your body. In my case, I think I now have little pieces of thread scattered throughout my body. The "pulling" is maintaining the connections developed in zhan zhuang while moving. Move too slow, you fall asleep or trance out. Move too fast, you can't maintain the attentional/intentional/fascial kinesthetic connection.
In Wujifa Zhan Zhuang practice, we notice and point out gaps or breaks in feeling fascial connection. I've noticed that these gaps or breaks typically appear where there is chronic muscular tension, which in a real beginner to the mind-body arts, is everywhere. Hence, why imagining that you are "pulling the thread" takes you down the wrong road.
Another common error that beginners make when learning Silk Reeling exercises is to not see nor understand the transition from zhan zhuang stance to silk reeling. In zhan zhuang, you are standing. In silk reeling exercises, you are shifting from side to side. So a great place to start, is to learn how to correctly shift from side to side, learn how to liberate your kua from its chronic stuckness.
A really excellent article and video that focuses specifically and explicitly on this basic, foundational skill can be found at:
Keys for Developing the Inguinal Crease, aka, Kua with Wujifa Side to Side Practice
The process of side to side allows a very specific focus to guide people in making progress towards understanding the inguinal creases which is so very helpful in deeper discoveries of full-body movement and practice.Here is the "Wujifa Side to Side Inguinal Crease Basic Training" video:
Interestingly, practicing this side to side exercise has also helped deepen my awareness in my zhan zhuang. When I practice side to side, sometimes I will rest my knees against a table or other furniture to remind me to keep my knees fixed in space. This helps get the kua opening and closing. The other sticky point is that the hips tend to turn as I shift. This of course is due to chronic muscular tension. To help this, I will practice shifting side to side with my back end against a wall or table top. Another problem I've had is that the top will lead or get ahead of the hips. Remember the principal, movement is generated by the legs. The top needs to rest on the hips but not in a locked manner. Let the hips "lead" but everything moves together.
When I began this side to side exercise, I really didn't feel much of anything. Now, with practice, I feel a very obvious "twining" movement in my lower back as I shift. This simple exercise can really benefit your silk reeling exercises!!!
Further Reading: Silk Reeling Exercise and Silk Reeling Production. This brief article considers parallels between A) silk reeling for the production of silk and B) Silk Reeling exercise.