The first step is identifying what type of wallpaper is on the wall. There are actually a large number of subcategories to choose from; however they can all be broken down into four basic groups. They are fabrics, vinyl/acrylic, colors, and patterns. There is also a duplex category which covers all wallpaper which utilizes two groups of materials. The correct cleaning method will depend upon what type of material the wallpaper is made of.
One of the most commonly found types of wallpaper is vinyl coated. It features an acrylic or vinyl coating over the surface. In general, is very resistant to stains and can be easily cleaned. While it can be lightly scrub, it is important to never use an abrasive cleaner or rough surfaced sponge. Being overly aggressive significantly increases the risk of damaging it.
An option which is becoming more popular is solid vinyl wallpaper. It is most often found in laundry rooms and playrooms because it is highly resistant to water, grease, and other types of stains. It can be cleaned more aggressively than vinyl coated wallpaper, although abrasive cleaners should still be avoided.
Another popular type of wallpaper is coated fabric. It falls into the duplex category. Fabric is bonded directly to the paper and normally has a vinyl or acrylic coated surface. It is also more susceptible to moisture damage and staining. While it is durable, it should only be cleaned based upon the manufacturer's directions to prevent damage.
The final commonly found option is plain paper. Plain paper remains popular because they can be embossed easily. There is no limit to how plain paper wallpaper can be designed and manufactured. While it is often the most beautiful and most expensive, it is also the most delicate. This makes it extremely risky to clean with any type of moisture or abrasive. If cleaning is necessary, follow the manufacturer's specifications. Normally, a cotton cloth or soft sponge is the only material which can be used to clean it.
Cleaning wallpaper will always be a tricky proposition, even with the most durable options. Ideally, the manufacturers warning and recommended cleaning procedures will be available. They can often be found online. If this is not the case, start with the least abrasive options and slowly step up to more abrasive solutions until it is clean.