Before beginning, turn off all power to the ceiling circuits and place a sign on the breaker box that reads "do not turn power on!" Put painter's tape on the wall to mark the position of the ceiling joists, making it easier to align the drywall with the joists. Close all doors to the work area and seal them with painter's tape.
If the wall isn’t straight, snap a chalk line four feet away from the wall as a guide for the first row of drywall; fill in the extra space with drywall pieces. Start with open rafters. Layering drywall can trap moisture that can ruin a ceiling
Press the drywall in place over electrical boxes then lower it and cut out the indentation with a spiral saw.
Finish with drywall tape and three coats of compound, sand in between coats. It is critical that you allow each coat of compound to dry for 24 hours and sand it smooth before applying the next coat. Add a fresh coat of paint and your new ceiling will look great for years to come.