You are not alone. This is probably the one exercise that most people have difficulty with. Well this one, and the whole idea of going into the emptiness.
This was the last one for me to start feeling anything while doing it. It was one of those thing, as a lot of SFQ has been for me, where I only realize I'm getting into it after I've been into it. Only after I stop working at visualizing and looking for feelings and just go through the movement completely relaxed and contented, do I find myself slip out of the exercise and say, "Hey, I was feeling X while doing this part and Y while doing that part".
As for instructions as to exactly what to visualize and feel, I believe Master Lin has purposefully chosen the level of instruction. This can be the most difficult movement to physically get coordinated and become relaxed and comfortable while doing. I think that the energetic experience for this exercise comes when you start to achieve the relaxed and comfortable mental attitude of just being in the exercise and feeling whatever you are feeling. When you stop trying to direct or to find anything.
I can now understand why Gallen has called this is favourite movement.
You might consider searching the forum on this subject, there have been some very nice threads on the subject.
The common advice of relax and do it, is probably most important for this movement.
I have played with visualization in this one a lot, and one that I particularly like is the image of being surrounded by energy like and fog or a playful mist. I'm not directing the energy so much as just playing with it. Scooping it up and throwing it. Hugging it and making a pillow. Inhaling it's sweet fragrance. Watching the wispy streams it makes as my hands sweep through it.
Although, I've add this one imagery I've used I think is all about doing the exercise and being in the now.
You are perfection.
Iam2 
