Hanging drywall on a ceiling is a difficult project, even for two people working together. If you're trying to do it alone, it may seem impossible, because one person can't realistically hold the 4-by-8 feet sheets of drywall up to the ceiling with one hand while you screw it in with the other. The solution is a drywall lift, which is simply a brace to hold the drywall in place while you attach it to the ceiling joists. You can rent a drywall lift made for that purpose, or build one yourself in about five minutes.
Measure the height of your ceiling, from the floor to the ceiling joists (or to the plaster surface of the ceiling, if you're drywalling over plaster).
Cut a 2-by-4 the length of your ceiling. Cut a second 2-by-4 that's 3 feet long.
Lay both 2-by-4s on their narrow edges, in a "T" shape, with the short board forming the horizontal span at the top. Use a screw gun to drive three or four screws through the face of the shorter board and into the top end of the longer board.
Lean the finished drywall lift against the wall under the area of the ceiling that you're going to drywall. Position it so it's standing up in a "T," with the 3-foot horizontal span positioned a few inches under the area where one 4-foot side of the 4-by-8 sheet of drywall will hang.
Lift the sheet of drywall and place one 4-foot side on top of the 3-foot horizontal span of the drywall lift. Holding up one end of the drywall with one arm, reach out with your other arm, grab the vertical span of the drywall lift, and pull it toward you. Jam the lift under the drywall to hold it to the ceiling, moving it toward the middle of the sheet as you do. Adjust the sheet on the joists, as necessary, then attach it to the joists with drywall screws.