This is more a request than a tip, but it will help everyone. If the door was closed when you arrived, close it when you go in, and close it when you leave. That simple.
Every afternoon, on my way home from work, I pass a small house on the side of the highway. For most of the year, there is no activity here, but the odd once in a while, I see people camp there. Are they the owners? Who knows? But most of the time, when I go by, the door is closed. During the winter, no one ploughs the driveway, and the door is closed.
Sometimes, however, I see footprints leading in from the highway, and the door is wide open. No car around, so it's not that someone's in there at that moment, but clearly they were and then left without closing the door behind them.
Here's the thing. An open door calls attention. People notice it. You did. I did. If you're inside, it could call attention of someone passing by, like a cop, or the property owner, and then they decide to check it out. In some cases, they might even lock it. Then you're screwed.
Second, it keeps animals and the elements out. Water, snow and raccoon crap do a lot to damage a building. By closing the door behind you when you leave, you're showing respect for the property, and helping to preserve it for the next explorer who comes along.