After the first strip has booked a proper length of time, take it up on your scaffold or ladder, unroll it, undo the first fold and then peel back the top to free that end. The strips are long and difficult to manage at full length so leave the bottom end booked for the moment.
Position the top up to the ceiling as needed, leaving a couple inches above for trimming and making sure the pattern's in a pleasing position. Line up the edges with the plumb lines on the wall and use a smoothing brush to apply the top of the paper to the wall. If you see then that you missed the marks, don't try to push it back into position.
That can stretch the wet paper out and leave gaps at the seams later on when the paper dries. Instead, pull the paper back off wall and reposition it.
Once the top is straight, peel off the bottom half of the paper and brush that into
position on the wall, making sure it lines up with the plumb lines. Then go over the paper again with the brush to remove any air bubbles or wrinkles.
Raise the paper off the surface and re-lay it if necessary. It won't affect the paste's adhesion.
You could trim the top and bottom at this stage but it's usually more efficient to get a few strips up and then trim them all at once.
Before moving on, though, use a wet sponge to wipe any excess paste off the surface of the strip. Remember, though, that not all papers are sponge-friendly so follow the instructions in this area as well.
Hanging the second strip (and the rest of the strips) will follow the same pattern as the first one. But now you need to worry about seams.
Actually they're not as much of a problem as people make them out to be. Just make sure the edge of the second strip butts up to the edge of the first one and that the pattern is matching properly from piece to piece. Don't leave any gaps and don't overlap them at all. Finish the strip as before, brushing it smooth and then sponging off excess paste.
There are tools known as seam rollers which are designed to roll over seams and firmly apply them to the wall.
But people often overuse these tools, rolling the seams over and over and over again. What that does is press the adhesive to the surface, leaving very little below. That gets sponged away, and there's nothing left to bond the seams to the wall.
So if you use a seam roller, do not press down too hard and do not roll a seam more than once.
Trimming Top & Bottom
Whether you trim each strip as you hang it or wait to do 4 or 5 at once, the technique is the same.
Use a broadknife (the 4-6 inch wide kind used for spackling or drywall joint compound) first to crease the paper where the wall meets the ceiling or the floor base to set up a straight cut.
Then, with one hand, set the blade of the broadknife in the crease at one end of the paper.
With the other hand, run the cutting blade along the broadknife, using it as a guide and making short cuts no longer than the width of the broadknife.
Make sure the broadknife is positioned between the wall and your cutting blade to protect the wallpaper if your cutting blade slips.
Reposition the broadknife for each cut till you get to the other end of the paper.
Then wipe the area with a clean sponge to clean off excess paste.