Entire books have been written on the subject of composition and it’s difficult to do the topic any justice in a single post. However, for those of you who are just starting out, I’ll offer two suggestions: Fill the image with your subject and consider the ‘rule of thirds’.
If you find that your subject is only a small part of your photo, you’re not alone. Try zooming in, getting closer (or both) and fill the image with your subject. Feel free to experiment and don’t always feel that you have to include the entire animal, person or building in the image. You also may be happier with your results if you shoot from the subject’s height. For example, if you’re photographing a child or pet, try getting down on the floor and shooting parallel to the floor or even slightly upward toward your subject.
Virtually every book on photography discusses the ‘rule of thirds’, which really should be called the ‘loose suggestion of thirds that works most of the time’. In summary, if you divide your viewfinder in thirds, both horizontally and vertically, the dividing lines will have four intersection points. Placing your subject at one of these points will often give a more pleasing result than placing the subject in the center of the frame. With people, experiment with placing the most important part of the image, such as the person’s eyes, at one of these points. When shooting landscapes, consider aligning the horizon with one of the horizontal ‘third’ lines rather than placing it in the middle of the image. This technique works most of the time but consider it an option and don’t feel bound by it.