Because flat wall paint is delicate, Franklin Painting suggests that cleaning always begin with the gentlest technique possible, which is to use warm water. Then, escalate to more aggressive cleansers until the stain comes out. In the worst cases, the wall may need to be repainted once the dirt has been removed.
Using a lint-free cloth soaked in warm water, start by gently rubbing the dirty wall. If the stain does not show improvement after a few minutes, move to a melamine-foam sponge, such as Magic Eraser, blotting periodically with a clean towel to remove residue. Bob Vila also suggests using a paste of baking soda and water, or diluting vinegar, ammonia and baking soda in a gallon of warm water to use as a cleaning agent. Other techniques should be tested on an inconspicuous painted spot prior to use. If the melamine foam does not work, use a gentle foaming cleanser. Spray it on the wall, and let it sit for several minutes. Then, wipe it off. Next, try a mixture of laundry detergent and water. If all these techniques fail, the affected area probably needs to be repainted.
Never use any tool harsher than a soft cloth to remove stains from walls. Rough sponges or scrub brushes may wear off patches of paint, often leaving behind a rough, damaged surface that needs to be treated before repainting. If repainting the entire wall is necessary, satin paints are just as appropriate indoors as flat wall paint, and are much easier to clean.