How: I decided to be more systematic on the folding before weaving, this is how I fold:
| Folding from the right, using  a weight to hold in place  | 
| Folding from the left side | 
| Folding the left side on top of the right, forming a pocket on one side  | 
| ...and folding a package to move to weaving | 
And now to the weaving. One time on the top, and back again underneath, and inserting into the pocket:
Reflection: Using clothespins to hold the folding in place is a hit (better then a weight - the pins can follow to the weaving. Also hear I cut off some 10-15cm in the end before inserting in to the pocket.
Special for my frame: As my frame has an extra enforcement (early prototype) in the middle I have skipped going down under the mid wire - every second weft will have a 3 grid wide part in the middle, but this goes only for my frame, nothing to worry about for other frames out there...