Histogram

“The first thing to realize, though, is that it’s not always necessary to use the histogram. In fact, selective use is best. Few if any photographers look at the histogram for each and every photo they take. In the majority of instances, your camera’s meter will accurately and precisely set the correct exposure for the scene.
But you should check the histogram when a scene’s lighting is especially tricky; when there are areas of deep shadow and bright light in the same scene; and when you’re going to take a series of images in the same setting and want to be sure your exposure is right on target.” [Nikon]

How to Use Your Camera’s Histogram
Understanding the Histogram
Perfect Exposures from Histogram through Lightroom