I would spray the drywall mud on your ceiling with a light coating of water from a spray bottle and scrape it loose with a 12" drywall trowel. Have plastic down on the floor. When it gets wet, it will start falling down. I assume you are talking about the standard stipple ceiling which is thinned out drywall mud rolled on with stipple roller and not a popcorn ceiling.
Make sure the drywall is completely dry for a few days before priming with a drywall primer and then painting.
Check this site. http://www.drywalltextures.com/texture.htm