Vacuum large chunks of dust and cobwebs down using the vacuum cleaner hose attachment.
Use a clean broom to knock away additional spots of dirt, dust or cobwebs. Before you begin, make sure the broom is either new or clean because you don't want to transfer extra dirt from the broom to the ceiling.
Using brisk, firm strokes, start in the corner and work your way from one end of the room the the other and clean the entire surface of the ceiling. You'll essentially be sweeping the ceiling the same way you would sweep a floor.
Take a damp sponge mop head to wipe any areas gently that did not get clean with the broom. Make sure the mop head is slightly damp and not dripping wet or the dripping water will make a huge mess on the floor and possibly give the ceiling water damage.
If the ceiling is stained, you can mix a solution of half bleach and half water to put on the mop head.
Lay a tarp on the floor and on any furniture in the room if you are using bleach to avoid stains if anything drips down.
Touch up in between full-out cleaning sessions with a long-handled feather duster in the corners and areas where cobwebs and dust seem to build up the most.