Different types and qualities of paint greatly affect how you clean a wall, as well as how clean it will come. There are generally four types of paint finishes you might encounter:

Baked enamel (most appliance finishes), epoxy enamel and automotive paints:
These paints are durable and pretty stain-resistant. Dirt typically cannot penetrate the hard-finish. These types of surfaces can withstand scouring with mild abrasives and can also handle heavy-duty cleaners and degreasers when necessary. With these finishes, you need to be most careful of scratching or dulling the finish by using harsh abrasives, steel wool, colored scrub pads and strong solvents.

General-purpose enamels:
This type of paint is the most common found on interior walls, especially kitchen and bathroom walls. This type of paint is pretty stain-resistant and can also handle moderate scrubbing. You should be careful, however, that you don't use abrasive substances or colored scrub pads, as this finish can be scratched. Most of the time, you should use a neutral cleaner solution and a white, nylon-backed scrub sponge. Only use heavy-duty cleaners or abrasive cleansers when you're willing to take your chances on ruining the paint. Make sure if you have latex enamel paints that you don't leave them wet for more than a minute or so. Oil-based enamels are more water-resistant. Keep in mind that gloss enamels are the most durable and washable, followed by semi-glosses and then satin finishes.

Latex flat:
This type of paint, which is a pretty common household paint, is not as washable as enamel paints. When you use heavy-duty cleaners or scrub the surface hard, you run the risk of removing the paint along with any dirt. Be sure to use mild detergents and gentle scrubbing, and don't let any solution sit on the surface for more than a minute.

Exterior paints:
Obviously, this type of paint is mostly used outside. These paints are typically oil-based or latex, and should be scrubbed only with a mild detergent and then rinsed with a hose. You may need to use a long-handled brush for hard-to-reach areas or stubborn spots. Some people like to use pressure washers on the outside of their homes, but these, along with other harsh chemicals, can loosen the paint. These should be used with caution.