To score the surface, get hold of a perforator tool for a couple of quid from your local DIY store. It's a small spiked wheel with a handle that you roll over the wallpaper to prick holes in it. (It looks like a Mexican rowel spur). It's certainly faster and much easier to use than a knife, with less chance of damaging the wall surface.
Use a spray bottle with Cruella's suggestion of a little washing-up liquid added to the water. Adding vinegar would work too, since these liquids improve the wetting effect of the water.