There used to be an old saying, "to wallpaper over your problems." Nowadays many wallpapers are so thin that professional paper hangers needs to prepare and smooth the wall as if they were preparing to paint. If you read my "Types of Wallcoverings", make a note that fabric backed vinyl is the best material type for covering up rough walls or cracked walls--- especially if the fabric backed material is heavily embossed and matte in finish. If the walls are really bad there are many different types of liner papers which act as an underlayment and pad the wall. Lining the walls to take care of roughness requires either polyester spun liner paper or thick non-woven liner paper. Nowadays grass cloth has become popular again and I don't think there's anything better than natural, thick grasscloth to cover up rough and problem walls.