Walls may require some preparation before painting / papering.
Clean down walls using Auro Plant Soap
Fill internal walls using the Auro or EarthBorn Fillers (external walls - only use the EarthBorn filler)
The wall fillers especially are excellent as they remain workable when dry, so you get a lovely smooth finish, but one that can be sanded back easily if one's DIY skills are not so professional!
X-Tex will remove old artex easily
New or ageing plaster can be sealed using a breathable Auro Plaster Primer
Use earthBorn Isolating Primer to seal in oily stains before painting