Dig out the area in which you intend to plant, going slowly and carefully as there will obviously be electrical cables beneath the surface. While you won't break these cables with careful, shallow digging using a trowel or a spade, plunging in with an electric hoe or incautious deep digging could be very dangerous.
Plant small flowers or shrubs near or around the power box. Don't plant thorny bushes, thick bushes or trees that will grow into impenetrable obstacles, because meter readers still need to be able to clearly access and view the power box. Most power companies will ask that you remove or prune such plants.
Move large shrubs or tall trees far enough forward to leave semi-concealed but clear access to the power box behind the plant. Check by inspecting the box yourself: if you can't comfortably access and read it, neither can a meter reader. Make sure to explain to your power company or meter reader how to access the box.
Water and tend to your flowers or shrubs as you would any other plant. Power boxes are designed to withstand harsh weather and environmental conditions, so there's no need to worry about electrical shocks or short circuits if you get the box a little wet while watering.