Measure the distance between a bottom corner of the outlet and the nearest wall. Choose whichever corner is convenient, left or right, but don’t forget which you chose.
Measure the distance between the bottom of the outlet and the floor.
Mount the drywall, installing drywall screws only around the edges to attach the board to each wood stud. Hold off on installing screws in the interior portion of the board at this time.
Find the location of the bottom corner of the outlet, using your earlier measurements. Mark the spot with a pencil.
Insert a keyhole saw or the bit of a drywall router at the pencil mark. Cut around the outer edges of the outlet box, keeping the hole as small as possible. If the hole is too large, the outlet plate you install later won’t cover the edges of the hole.
Install drywall screws in the interior portion of the board after you uncover the buried outlet.