On passive building entries where you have approached quietly and have the first entry door opened:
stop...
listen...
and smell the air.
After anywhere from 10 seconds to a minute or more, many suspects and potential ambushers will get nervous and may move or make other sounds you can use to pinpoint their whereabouts. Once you move in, only use your flashlights in brief bursts until you find available light switches to illuminate a room.
Remember to take cover before you light up a room or building. Then wait again for sound or movement before continuing.