Check your local building codes before starting. Most municipalities require at least an 18-inch deep trench, while many require 24-inches.
Start your trench against the house, on the wall nearest your electrical circuit breaker box. Drive a wooden stake in at this point and one where you need the wire to resurface. Tie a piece of mason's twine between these two points to mark the line of your trench. Use a sharp shooter, or narrow bladed trenching spade to dig a trench along this string, 24-inches deep.
Lay cable into the trench, leaving enough slack at the house and the terminal end to feed through any conduit through the house wall to make the needed connections. Use UF, or Underground Feeder wire, which is rated be installed without further insulation or conduit.
Bury the trench with back fill from the dirt you removed from the trench, making sure the wire stays on the bottom of the trench. Have an electrician inspect your work and make the connection to the house breaker box and any connections up to the junction box on the opposite end.