Before you attemp to clean anything, first ask these questions and take precautions not to further harm the finish.

HAS THE FINISH HAD AMPEL TIME TO CURE? After the paint is dry to the touch, most paints need at least 30 days under normal drying conditions to properly cure and harden and arrive at its final sheen. Cleaning could cause damage to the paint. Moisture and other chemicals may penetrate and stain or bubble the film or the surface could be easily marred, scratched or even inadvertently removed.

WHAT ARE YOU TRYING TO CLEAN OFF? Knowing what the stain is, is half the battle.

WHAT SHEEN IS THE PAINT? Finishes of a higher sheen are more easily cleaned than a flat sheen paint. Lower sheen paints can be easily burnished (a different sheen spot made by rubbing) by even rubbing lightly with a sponge. This could leave a spot just as ugly as the one you were trying to clean. 

HIGHER SHEEN PAINTS AND ENAMELS can resist scuffing better than flat paints. A scuff with no color left behind may only be a burnished spot which is a sheen inconsistency spot and is impossible to clean.

NEVER AND ALWAYS Never scour a painted finish with any abrasive cleaner or scrubber. Never mix cleaners such as bleach and ammonia. Always read the label on the cleaner. Always try the mildest cleaning method first. Use the harshest chemicals only as a last resort before repainting. Some chemical cleaners that may work on a certain type of finish may be a stripper for other types of finishes.