Composition means arrangement: putting together elements to make a whole. Just as speakers of a language must learn to put words in order to communicate verbally, photographers must learn to arrange the elements of their photos in order to communicate visually.
Good composition feels right when you look at the finished photograph. The eye and the mind have a preference for certain arrangements. When this arrangement is present in a photograph, the viewer's eye will stay in the photograph longer.
When you're taking a photograph, try not to think about just the objects in the photo. Try to look more 'abstractly' at the scene and recognise shapes, shadows, forms, lines etc. This is a skill that can be cultivated over time with practice. Although no one can give you the rule to follow in any given scenario (there are simply too many possible scenes to photograph--that's what makes photography so special!), there are some principles you can start to think about that will improve your composition. Looks out for these visual elements in your photos, and remember to take lots of photos. When you look back over your photos, compare the compositions and see the effect of each.
Look for converging lines such as roads, railway lines, paving stones, railings and shadows. These lead the eye across the picture and into the distance, making for a more dynamic shot. This technique often works well in a wide-angle photo.
Try to find repeating or rhythmic elements such as anything in rows – people, trees, cars – or any repetitious arrangement. These patterns are restful to the eye, but the slight variations make the composition lively and interesting. This works well with photos taken in telephoto mode or taken with a long (telephoto) lens that allows a far-away view.
Overlap elements in the scene to partially hide your subject – creating a sense of mystery. You’ll also notice a greater sense of depth – space receding into the picture. This works well with photos taken in telephoto mode or taken with a long (telephoto) lens that allows a far-away view.
Use frames within the picture: trees, people’s arms, doorways – these are all framing devices which concentrate the viewer’s attention on the point of interest. Sometimes adjusting your position only slightly is all it takes to use one object to frame another.