Sometimes you get lucky. The more you go out to shoot, the better your chances are of this happening. It's a good idea to bring your camera with you all the time. I started doing this about five years ago, and as a result have been able to capture some images that would otherwise exist only in my memory.
For the shot above, I was showing my folks around Marble, Colorado on an autumn afternoon. We started driving back to my house when I saw a plane taxiing to one end of the small airstrip there. There's very little activity at this strip, so I recognized this as a rare opportunity. We pulled over at the far end, and I positioned myself so the plane would fly right over my head. As the plane approached, I fired off half a dozen shots. This is my favorite.
In an effort to capture the amazing colors of autumn in the mountains, I got up early every day for over two weeks and drove to the far side of Beaver Lake in Marble, Colorado. On this particular morning, it was pretty clear when I left home, but some rain clouds were moving in quickly from the southwest. The sun rose over the mountains to the east as the clouds and rain reached Marble, creating the conditions for these two photos. The first is the light hitting the rain falling to the valley downstream. The next one is the rainbow that formed when the rain reached the far side of the lake. I especially like how the base of the rainbow is on the colorful mountainside aspen trees.