Remove all wall hangings, blinds, outlet and light switch covers, mirror, and wall-mounted light fixtures.
Patch and sand any nail holes with Spackling Compound. Allow to dry, then sand smooth with a Sanding sponge.
Cut your strips making sure that the pattern shows the way you want it to. For example, don't cut a bird design (or similar) in half at the top of the wall. Allow for at least an extra inch at the top and bottom. And make sure you also allow for any pattern repeat before cutting your next strip. Measure twice, cut once!
Activate the paste. I used the "glissade" wallpaper which requires spraying the wall and the back of the paper with water. I used a continuous spray mister that didn't require as many pumps as a regular spray bottle. NOTE - Some papers are "paste the wall" type and for those, you'll apply your paste with a roller or brush. Peel and stick requires no paste.
Use your level to make sure each strip is hung straight.