Turn the chair upside down to gain full access to the legs.
Place a surface mount brace along the bottom of the chair seat extending onto the chair leg. A surface mount brace is a metal brace that resembles an "L" bracket, but is much thicker. Surface mount braces are short sturdy brackets, made specifically for furniture bracing.
Hold the brace in place and use a pencil to mark the screw holes on the leg and chair seat. Surface mount braces come with pre-drilled holes.
Drill pilot holes into the marks 1/4-inch less than the thickness of the chair seat and chair legs. Drilling in closer than 1/4-inch can cause the screw to poke through the seat and the wood to split. Pilot holes are guide holes for screws.
Place the mounting brace in place, lining the pilot holes up with the holes on the brace.
Screw the screws through the hole on the brace and into the wood. Use screws 1/4 inch shorter than the thickness of the wood.