As others have said being polite and friendly works wonders. A couple of my own experiences are as follows. Many years ago early morning fog across the south of England had lots of the early morning arrivals diverting North and Teesside (now DTV) received a couple of BA 747's. Trying to take pictures through the fence into a bright morning sun was impossible. I was having a chat with one of the Security Chaps and explained my problem. "Walk round to the Departures Gate in the Terminal" and meet me there he said. Minutes later I was escorted through Departures and out onto the Apron, underneath BA747 Sir Francis Drake and allowed to take my Pictures with the Sun in my back !!.
Another time my Wife and I where at the Canadian Warplane Heritage at Hamilton, Canada. It was a quiet time, mid week and off season. The Lancaster was in the hangar on Jacks with a couple of Engines removed. We where behind the Rope Barrier taking pictures when one of the Mechanics heard our English voices and asked where we were from. When we told him we had stared our journey from RAF Middleton St George (Teesside Airport) the barriers where lifted and minutes later we where in the Lancaster Cockpit. (bit of a struggle) Brilliant Experience. Later we where treated to Lunch and Coffee in the Canteen.
It pays to be nice, friendly and courteous.