Fill the steamer unit with hot water and allow it about 30 minutes to heat. Cover your floor with dropcloths, remove the faceplates from the walls you'll be working with and cover the outlets with electrical tape to protect them from liquids.
Use a wallpaper-perforating tool such as the "Paper Tiger," which is a roller with small spikes that will perforate the paper. This will allow the steam to penetrate the glue more readily. Be careful not to press too hard so you don't perforate the wall surface. If it happens accidentally, you'll need to fill the nicks with spacking compound.
Wallpaper steamers tend to drip hot water, so you'll want to wear rubber gloves. Place the steamer on the surface of the wallpaper and hold while the steam penetrates and softens the glue. The more time you dedicate to steaming, the less time you'll have to spend scraping.
Once the steam has softened the glue, begin working at a seam or the edge of a perforation to remove the paper by scraping with the wallpaper scraping tool, a plastic putty knife or a drywall knife. Apply more steam as needed and continue scraping until the wallpaper is removed.