With people the eyes are the most important for they are what connects the viewer to the person in the photograph. A simple shift of the eyes combined with a frisky expression says it all. It's not always a matter of luck to catch these kinds of moments, but luck certainly helps. Anticipation and being observant are the two ingredients most necessary to consistently capture these great opportunities.
Action shots are another category of photography that requires an element of timing. Whether it be sports related or moments with a great deal of movement, timing is the critical element in capturing the story of the moment. The trick is to incorporate not only the movement, but all the supporting elements as well. Wildlife action shots are perhaps the most difficult to capture simply because you must wait for the wildlife to perform in front of you, and they seldom ever cooperate in such a way as to accommodate what you want to capture.
Your presence alone will often alter their behavior and in many cases simply spoil the opportunity. It takes a great deal of patience and an understanding of the habits of the wildlife you are photographing. Cold fingers and numb toes will become a common predicament when photographing wildlife in the winter. But, to get the close in, compelling shots, you must be willing to alter your situational comfort to meet the wildlife on their terms.
Timing also includes not only those precise momentary captures, it also includes a broader more seasonable elements and this includes time of day. Finding an interesting subject is only the beginning of timing a great photograph. You must learn to think beyond what you are looking at and project how the scene will appear at different times of the day or even in different seasons. A snapshot of a windmill in the middle of the day is not necessarily a very compelling shot regardless of how interesting the subject. Move time forward a few hours and catch it at sunset and this rather ordinary subject now becomes engulfed in a magical moment of light.
Swap out the windmill and insert a tree and once again the timing of the shot generates a eye stopping image. This tree if taken in the middle of the day would simply be a photo of a tree, but add in a bold summer setting sun, it becomes an iconic symbol of what the art of photography is all about.
Timing the shot as a photographer becomes a process requiring a great deal of practice and observation. Knowing and understanding how your camera reacts to light and having a command of your camera is also critical because you do not what to be guessing about your exposure when those often fleeting moments present themselves. Great timing combined with a commanding grasp of how your camera does what it does will lead you toward capturing amazing images that stir the imagination.