What are the three most essential steps in securing and controlling a building or premise?

"From my experience in providing security services for buildings, I would say that the three most essential steps to securing and controlling a building and premise include checking to ensure the video surveillance systems are working, that there is adequate lighting, and there are security officers strategically placed near entrances of points of vulnerability."

"My instinct tells me that the essential steps to securing a building come in the form of making sure that areas are well-lit, ensuring there is a good video surveillance system with strategically placed cameras, and a building entrance system controlled by keypad, fob, or swipe card. I look forward to learning more from my training at G4S."