Composition is made up of a variety of elements; depending upon which books, online articles, or magazine articles you read. The key elements to a good composition are; your subject, the background, lighting and shadows, and color. In this blog I will discuss the first four elements; subject, background, lighting, and shadows. Color will be covered in a seperate blog entry.
The subject will be the main focus (pun intended) of your photograph. There are unlimited number of subjects for you to choose from; portraits, landscapes, wildlife, architecture, and sports are common for photographers. Placing your subject using the rule of thirds is a strong suggestion, not a hard rule that you have to follow. Yet, many photographers prefer avoiding placement of the subject in the center. The reason is that the photograph becomes ordinary and less interesting with center placement of the subject.
Background is what is behind your subject, which can be natural if you are outside shooting wildlife, sports, portraits, or nature. Backgrounds can also be manmade if you are indoors and have or making a studio. The key point to remember in appropriate background choice is not allowing the colors to overwhelm your subject or blend into the subject. Be cautious of photographing a person with dark hair or clothes in front of a dark background. The background can be blurred by using an fstop (aperature) of 1.4-5.6. Manmade backgrounds are mainly used in portraits and are either a blend or solid colors (white, black, grey, blue, red, or green–which is used with Digital backgrounds and photo editing programs like PhotoShop).
Lighting and shadows in your photograph can be controlled by using your flash, portable lights and reflectors to redirect the light onto or off of your subject. There are also screens you can purchase or build (plans can be found in some books and online) which will help diffuse the light–making it softer and less harsh. Artificial lighting is varied from florescent, strobes, monolights, on and off camera flash, and tungsten. Each of these lights will impact your subject differently, as each light has its own unique temperature. (This will be covered in another blog entry, with suggested reading list included).
This blog entry covered some introductory information and thoughts on composition. There are many more resources available online and in bookstores. I would recommend reading the following books to learn more: Digital Photography by Scott Kelby, Modern Photography by John Hedgecoe, as well as books and videos by Bryan Peterson (some of his videos can be found on Adorama TV).