Chiseling a recess -- called a mortise -- for a door lock plate is one of those jobs that's very simple in theory but also very easy to mess up. If things don't go well for you the first time, your lock will probably work fine after a few adjustments, but you'll likely have to view the evidence of sloppy work for the life of the door. So, take the time to mark and cut carefully. Whether you're installing a lock plate, also called a strike plate, for a deadbolt lock or a standard lockset, you first must install the lock or lockset onto the door, following the manufacturer's instructions.
Close the door, and look for where the lock bolt or latch bolt contacts the doorjamb. Mark the precise center (top to bottom) of the bolt onto the inside edge of the jamb using a pencil. Use a combination square to transfer this center mark across the face of the jamb -- that is, onto the flat strip between the inside edge of the jamb and the door stop.
Measure and mark a line along the center (side to side) of the jamb strip, intersecting the line made in the preceding step. At the line intersection, use a spade bit to drill a hole for the bolt as directed by the lock manufacturer. For flat-sided deadbolts, you typically drill two overlapping 7/8-inch holes centered about 5/16 inch above and below the horizontal center line.
Position the strike plate on the jamb so it is centered on both lines. Score around the plate with a sharp utility knife. Using a sharp 1-inch-wide chisel, cut a series of parallel lines into the jamb about 1/4 inch apart, staying within the scored lines and holding the chisel perpendicular to the wood.
Remove the waste wood with the chisel -- bevel side down -- held nearly parallel to the jamb. Clean out the mortise until its bottom is smooth and flat and at a depth exactly equal to the thickness of the strike plate. Test-fit the plate as you work to check the mortise depth.
Drill pilot holes for the strike plate, and fasten it to the jamb with the screws provided.