Additional receptacles can rarely be added to existing circuits without causing an overload.
To install a new 20 amp receptacles properly, 12 gauge grounded Romex type wiring must be run from the circuit breaker panel to the receptacles. The wire entering the breaker panel must be held by a wire clamp and be stapled to the wall within 18 inches of the panel.
A new 20 amp circuit breaker must be installed in the panel. Do not connect the new wire to a breaker that is already in use, doing so would cause a double tap.
The new wiring must be secured, wiring can not be run in an exposed manner through habitable areas of the building. Wiring must be secured to walls or ceilings. Wiring in the living areas of the property if exposed must be in conduit.
The new receptacles must be secure in a box, with a cover plate. All bathroom, kitchen, exterior, and garage receptacles must be Ground Fault Circuit Interrupt (GFCI) protected.
NOTE: Electrical work should be done by a qualified electrician.