Looking on the back of the camera to see if you got a shot properly exposed can be misleading. The LCD may not be calibrated showing a too dark or a too light image. Or the sun hitting the LCD can be laying tricks on you.
Yet there is a tool, that is often ignored that can give you a very quick and good indication if you exposed correctly – The Histogram.
In a nut shell, the histogram is a graph that show how many pixels of each brightness level are present in a frame. John Greengo of CreativeLive give a full back to basics course on photography, in this installation he discusses the Histogram in very easy to understand manner.
Generally, John mentions that you would want a histogram that looks like a mountain with a strong peak in the middle and a slope that goes out to either end. While specific captures may be unique, (such a capturing snow, or night shots), a strong peak on the right may indicate an over exposed image, while a strong peak on the left may indicate an under exposed image.