Remove any previous fabric from the arms of the chair. Gently pull the staples apart from the frame using a flathead screwdriver or needle-nose pliers. This fabric can be used as a pattern for your new upholstery fabric.
Lay a piece of muslin cloth over the arms of the chair to make a pattern. This is only necessary if you were not able to preserve the previous fabric or you are creating a chair from scratch. Trace the shape you need on the cloth with a pencil. Lay it flat and add one inch on all sides. Cut out your pattern.
Pin your old fabric or muslin cloth to your desired upholstery fabric with straight pins. Trace around your pattern and cut out your piece. Position over the arms of the chair and adjust placement as necessary.
Cover the chair arms with upholstery foam if they do not already have any. Apply a spray adhesive and then a layer of cotton batting; the adhesive helps hold the batting in place. Using a staple gun, staple your batting directly to the chair frame.
Place the fabric over the batting, "walking" it around any curved areas by folding over like pleats and stapling in place. If your fabric is thick, you may have to cut short, narrow slits in the fabric to help it fall in place correctly.
Pull your fabric taut around the underside of the chair arms. If you apply your fabric too loosely, it will look misshapen. Staple directly to the frame with the staple gun. Leave a quarter-inch of excess fabric around the staples and cut off the rest.