Remove furniture and other items from the room. It is much easier to tape the edges of the ceiling in an empty room
Tape the edges where the ceiling and wall meet with blue painter's tape or masking tape. Blue painter's tape is easier to remove once the paint job is completed. Place the tape on the wall. Start in one corner and work your way around the room. Hold the roll of tape up to the line where the ceiling and the wall meet. Slowly unroll the tape, pressing it into the line with your fingers. Go over the tape with a putty knife, firmly pressing the tape into the edge between the wall and ceiling. This provides extra security.
Tape around the edges all the light fixtures in the ceiling with blue painter's tape or masking tape. If vents and electrical covers on the ceiling are not easily removed, tape around their edges as well.
Carefully remove the tape after the ceiling has been painted. It is best to remove the tape before the ceiling is thoroughly dried. Start at the corner of one wall and work towards the opposite corner. Don't go fast because it is possible to pull the edges of the new paint off with the tape. Pull the tape very slowly. Hold the edge of the tape between the index finger and thumb of one hand while lightly pressing the tape against the wall with the other hand. The added pressure helps the tape to come off without damaging the paint job.