After wallpaper is pasted, it is “booked,” which means folding pasted-side-to-pasted-side, usually sectioned off with the top 1/3 and then the bottom 2/3. Then the strip is taken to the wall and unfolded and then positioned and smoothed against the wall.
But when hanging a ceiling, which can be a much longer strip and with gravity working not with you but against you, I’ve found that accordion folds (see photo) make the strip much more manageable. Once the first section is in position on the ceiling, I use push pins to hold it temporarily in place, while I move along the ceiling, working the remainder of the strip into position, unfolding one section at a time.
Since I don’t have scaffolding, I set two ladders next to one another, so that I can step from one to the other (see photo), when enables me to smooth longer portions of the strip of wallpaper into position before having to get down on the floor and move the ladders further down the way.
Sorry – no pics of me unbooking those according folds or smoothing the paper against the ceiling … If I had taken my hands off the paper to pick up my camera, the whole strip would have peeled itself away from the wall!