The best thing would be to buy/hire a wallpaper steamer. If that's not possible, take off the paper with your scraper, which invariable leave the backing on the wall. Score the backing paper with your stanley knife then using a sponge, soak the walls with warm soapy water, leave it a few minutes and scrape off.
Mix a solution of one part fabric softner and two parts hot water and spray it on the wallpaper. Let it set for at least 10 minutes. It may take a couple of applications depending on how many layers of wallpaper. I leaves your room smelling good, too