Before beginning demolition, set up a dust containment system to keep debris centralized to the work area. Place tarps on floor, then seal the doorway by hanging a zipped plastic seal to the doorway. Measure out a sheet of plastic larger than the door opening. Adhere a single side of the zipper system to the middle of the plastic. Adhere the other side of the zipper system to the back surface of the plastic. Open the zipper and use scissors to cut the plastic down the center. Tack the plastic to the top of doorway and the surrounding wall, sealing the sides.
Move on to the removal of trim and facings. Remove the door using a pry bar to tear the door jamb away.
If you plan to reuse the door facings after demolition, minimize damage as much as possible. Use end-nip pliers to pull nails from the back surface of the trim to leave the front surface unmarred.
Before beginning any additional demolition, be sure to cut power to the room. A circuit breaker locator is a two-part tool to help you match the correct circuit breaker with the wiring. One part is inserted into the receptacle in question; the other part is touched to the circuits in the breaker box. A light will alert you to the correct breaker. Turn off the breaker, then move on to the removal of all surface-mounted receptacles and wires.
Note: If you're uncomfortable with electrical work, please call an electrician to perform any electrical work.
To minimize damage to the surrounding drywall or plaster, use a utility knife to score the paint where it meets the baseboard. Then pry baseboards loose. Use a small drywall saw to cut small sections of drywall away between studs. This will allow you to locate any hidden wires or pipes. Once you've visibly located any new wires, use an audible continuity tester to determine if the wire is "hot". If the wire is live, use the circuit breaker locator to find the correct breaker and shut down power to the wires.
Move on to the demolition of walls and drywall.
Check walls to make sure they aren't load bearing before removing studs. Use a reciprocating saw to cut through studs and remove wall. Next, remove old drywall or plaster and lathe, tearing it down to the studs in the remaining walls.
Avoid being aggressive during demolition and you'll minimize both damage and cleanup.
Cut new drywall to fit. Score drywall on one side with utility knife, then apply pressure at the score line until the drywall snaps. Turn the drywall sheet and clean up paper edge with utility knife. Secure drywall to the studs using 1-1/4" drywall screws spaced about 8" apart. Countersink the nails (holes will be filled with drywall mud in the next step).
For outside corners, use a metal or vinyl corner bead to create a true 90-degree angle. The corner bead provides a finished, protected corner. Cover the bead with a coat of drywall mud. For inside corners, use drywall tape, folding the tape in half and bedding into the mud with a 6" knife. Use a special inside corner trowel to apply pressure evenly as tape is applied.
Allow mud to dry, then apply a second coat using a wider 10" knife to "feather" the mud. When the second coat is dry, lightly sand the surface and use a topping compound (a thinner mud) to finish the seams and screwheads. After the third coat is dry, lightly sand with a damp sanding sponge until all surfaces are smooth. Finish the job with a coat of high-quality primer/sealer to prepare the surface for paint.