Composition isn't just how you choose to frame a shot. It's the process of arranging the things in your shot so that the viewer can more easily "read" your image. The idea of reading an image may sound strange (despite a picture being worth a thousand words), but just as some sentences are easier to understand than others, so are some images.
You won't find a single recipe or formula for good composition--and for every "rule" or guideline that you see, you'll encounter a great image that breaks that rule. Before you can start breaking the rules, however, it's a good idea to be proficient with them. Rather than give you a list of composition tricks (such as the rule of thirds and repetition) we'd like to encourage you to think about composition as the process of making your subject clearer, and your image less complicated. No matter what composition rules you follow, clarity of subject should always be your main goal.