Guerilla Lighting:
Guerrilla lighting is used when time is of the essence or when lighting equipment is unavailable. This technique is most often used in news reporting. The reporter has to shoot the interview, gather the B roll and go back to the station to edit the piece before the 6 O'clock news. So, she or he does not have time to set up the lights.
Still using the principles of 3 point lighting, the shooter looks around and finds existing lights to use.

Indoors:
Look for your primary light source and use the ambience light as the fill and back.

Outdoors:
The sun will be our primary light source. Remember to put the sun behind the camera or the subjects will appear as black silhouettes.