Hold the doors against the armoire where you plan to hang them. Make a straight line across the top of the doors using masking tape or light pencil marks.
Place the hinges on the doors with the doors facing the ground. Use two hinges on doors under 2 feet long, and three hinges on longer doors. Space the hinges evenly, with the top hinge leaving two to four inches above the hinge and the lower hinge leaving the same space beneath the hinge. Use a yardstick or measuring tape to line up the hinges on both doors so they hang evenly. The long leaf of the hinge will be screwed onto the doors.
Mark the spaces on each hinge where you will screw in the hinges.
Put the hinges aside and drill small starter holes in the doors where the screws will go. Avoid drilling too deep, or you'll put a hole in the doors.
Replace the hinges and screw the screws into the door through the holes in the hinges using a screwdriver.
Line up the doors with the straight line on the armoire one at a time. Hold the door in place exactly where you want it to hang and open the hinge so the small leaf is flush with the armoire. Mark the screw holes with a pencil.
Use a drill to make starter holes in the armoire where the hinges will go.
Hold one door in place and screw the hinge into the armoire. Repeat until all the doors are hung.
Check the top of the doors with a level. If one side is uneven or not level, adjust the door by unscrewing the hinge and moving the door into place, then screwing the hinge into place once more.