I suppose one of the most damaging of errors most people make when creating a photograph is to try to capture everything in one image. This almost never works in a composition as it tends to create a great deal of clutter that distracts from the main subject of the image. In fact, it often obscures the main subject so much that the image loses its focal point and becomes uninteresting.
As a photographer my purpose is to create order out of all the visual chaos. Sounds easy but it is not always so. The trick is to learn how to visually focus in on what is truly important. You do this by asking yourself a very specific question; What am I seeing that is truly capturing my attention?
Where does your eye keep going? More often than not if you can answer that question, you will discover the best solution to your photograph. When looking for the answer, the idea then is to simplify everything down to its basic elements and compose your image based on what you discover. You will find that by using less in your image you will actually create more. Doing more with less is a great way to learn how to compose images.
Isolating the most important part of your composition is an effective way to do more with less. I will often use a long focal length lens, something like 200mm to 500mm, to help me find and isolate what is most important. The long lens will by it nature create a blurred background and this alone will enhance that sense of subject isolation. However you can also isolate in other ways. Sometimes I will use a wide angle lens and use a dark or bland or uncomplicated background to isolate my composition. The sky for instance works well for this.
When trying to isolate your subject always think in the context of what fits. Simplifying your composition does not always mean your image will lack for complex details. What it means is everything that shows up is there for a reason and does not interfere with the composition. Nothing appears out of place. This does take some practice to develop your artistic eye, but is something even beginning photographers can grasp.
Doing more with less is a great way to develop your seeing skills. It is a matter of answering the question of what is most important about what I am seeing, then focus in on the answer.