It is not uncommon for people with marble floors in need of polishing, or honing & polishing, to speak in terms of "cleaning" the marble. You don't simply clean your way to a new, shiny marble floor. It is, of course, possible to just clean a marble floor. Get yourself a good quality specialty marble cleaning product, spray some onto the floor, and scrub with a floor machine and absorbent pads. But this may simply result in a clean but still dull and/or scratched marble floor. This is where you either take yourself to a marble refinishing school (there are at least a few), OR, call in a local, experienced, well-recommended marble floor professional to do the job for you. You pay him his rate; the customer pays you whatever the two of you agreed upon.