1. Measure and cut your wallpaper
2. Always have your wallpaper go continuously around a corner... don't have it stop at a corner or a dark "gap" will show when you're all done. To make this easier, crease/fold the wallpaper piece where the corner will end up.
3. Use an old magazine and lay a piece(s) of your wallpaper upside down on it.
4. Smear tacky glue all over the back of it, paying special attention to the edges.
5. Quickly go wash and dry your hands, or keep a wet rag handy to wipe the glue off your fingers before pressing the wallpaper into place.
6. Turn the magazine page, and you have another fresh surface for gluing the next piece!