The most useful tool in determining if the exposure you are taking is correct is the histogram. This tool can be made to show alongside of the picture as soon as taken or when reviewing the pictures on the camera screen. A histogram has five basic areas. Tall bars to the very far right indicate something that is bright white. Tall bars to the very far left indicate something that is black. The middle area is called the midtone area. The areas close to the far right or far left are the highlight area and shadow area, respectively. Another key tool for exposure is exposure compensation. This tool helps fight the camera which would normally turn something that was very bright or very dark gray because it reads the light as if it were an average scene. Exposure compensation allows the user to increase or decrease exposure by a specified amount of stops.
One of the most challenging aspects of nature photography is dealing with varying light conditions. A general rule is to avoid the direct light of the midday sun due to a loss of detail that is caused by the excessive contrast caused by shadows and highlights. Clouds help during the middle of the day but the best time is in the early morning and afternoon when the sun is close to the horizon. Front lighting is generally preferred for shooting animals in the early morning and late afternoon because it helps give the animals detail. The opposite would be backlighting. Backlighting can create interesting abstract photos such as a halo of light around the subject or a silhouette. Side lighting gives a feeling of movement into the picture and is most useful for landscapes on a large scale where shadows add to instead of take away from the picture.
A key tool to nature photographers in fighting ever changing light conditions are filters. The most popular filter is a polarizing filter. This filter can be used most of the time while taking pictures to help increase color saturation by reducing glare off of water and other surfaces that reflect a lot of light. They usually reduce brightness by one to two stops. Another type of filter are split neutral density filters. These come in different stops and are most useful for taking pictures of a colorful landscape with a bright sky. They are then used to darken the sky by the number of stops. If the landscape does not fit with the straight line of a neutral density filter, a graduated neutral density filter can be used.
Even with proper exposures and the right lighting and camera settings, there is still much more work to be done. Image compensation seperates the best photographers from the average ones. It isn't hard with a lot of practice to know how to make a good exposure, but the composition of an image is just as if not more important. There are seven rules of visual priorities listed in the book that can help compose an image: red is more attractive than yellow; large draws more attention than small; difference drows more attention than conformity; jagged lines are more striking than curved ones; diagonal lines are more attractive than vertical ones; sharpness is more attractive than blur; light is more attractive than dark.
A good exposure will not be very interesting if the center of interest is in the wrong place. The center of interest is the reason for taking the picture, and the purpose of the rest of the composition is to support the center of interest. Generally the center of the frame is not a good place for the center of interest because eyes travel to it first in the center and then there is nothing else worth looking at in the picture and it doesn't have any kind of movement for eyes to follow and really examine an image. A dynamic picture will lead to the center of interest through other interesting parts of the composition. The rule of thirds is good to follow, placing the center of interest one-third of the way from the top or bottom and sides.