Spread a tarp on the floor beneath the area where there is water in your ceiling. You can locate the location by a drip, a water stain or an ominous bulge in the ceiling.
Stand on a chair with a bucket and a drill. Drill a hole into the spot where the drip is coming from, or into the center of the stain or bulge. Pull the drill away and replace it with the bucket as soon as you penetrate the drywall, because water will come out quickly. Have someone standing by with another bucket so you can quickly switch buckets if the first one fills up.
Cut into the drywall with a sharp utility knife after the water has run out. Cut away a small piece to begin with so you can see into the ceiling and assess the damage. Cut away increasing large pieces of drywall until you have removed all the drywall that is wet or affected by the water.
Leave the hole in the ceiling so that air can circulate and dry the area. You can accelerate this process by placing a small fan in the opening.
Don't repair the hole until you have identified and repaired the cause of the water in your ceiling. If you don't repair the cause, it will happen again.