Learn the rules. Then learn to break them.
There are no rules!!! There are no "rules". There are elements and principles of design and composition. There are no set "rules". Lets repeat that about a million, billion, trillion times: "There are no rules".
The so-called "Rule of Thirds" is not a rule, but is instead a guideline that allows people a shortcut to placing elements of a composition in places where the eye tends to linger, and where tension will not be caused. Most of what people think of as rules are instead, shortcuts and typically accepted ideas about general ways to accomplish things. For example, in a portrait, it is considered bad form to leave 1/8 inch of top space on what will be an 8x10 sized portrait---that little top space or head space, will place the top of the head at the edge of the composition, which creates tension.
Composition is the most-effective or best utilization of the image area. Composition is arranging the elements using design principles to achieve a desired effect. Composition is the one thing that can be tremendously improved by studying the fine arts. A typical compositional blunder is to place a child in the middle of a horizontal image area, crop off the top of his or her head, crop really,really close to the chin at the bottom, and then to say, "I like it this way." That is the hallmark of the uneducated, unstudied, ignorant photographer--one who has absolutely ZERO idea of how to BEST use the entire image area. It typically results in 40% person, and 60% dull, uninteresting, irrelevant, and distracting background that does absolutely nothing to advance the composition, or to cause the viewer to want to look at the image for more than 1 or 2 seconds. I see that a LOT. Pictures like that show me that the photographer does not understand anything about composition.
In most of the USA, public school students have a very limited education in art. "Art" in public schools is typically really not much more than "crafts". Turkey hand-tracings, color-by-number drawing and painting, identical clone-like "art projects" where each student creates the same, basic piece of "art". That is not art education--that is "crafts". Performing the mechanical (filling in areas with colors, pasting on macaroni, drawing a hand-turkey,etc) without any education in the theory or principles is not really art education. But that is kind of what typical elementary school kids receive as their "art" education. So it is little wonder that by the time they hit high school, kids for the most part are not interested in "art". Art has been devalued in American education. It's not even Cliff notes--it's the back of the book blurb.
One thing that art education will teach a person is how composition and design are found everywhere. And it will teach a person that the world is filled with kitschy junk being passed off as "art". The worst part of this entire discussion, this discussion of the value of studying art, is that so,so many people with absolutely zero education in the study of fine art weigh in with opinions, *as if* they know what it (studying art) will do...it's as if somebody who has never flown in an aircraft tells you what flying will feel like, or what a person who has never left the city for more than a day tells you how you will feel after a 10 day foot trek along the Pacific Coast Trail... Listening to the points of view and arguments of people who have absolutely NO EDUCATION in a field of study is a dangerous way to form opinions. Would you listen to the opinions of a self-trained medical doctor operating with zero certification, zero courses, and zero understanding of the field of medicine? Art as a field of study is almost as old as medicine. We recognize the need for training in medicine in order to be qualified to talk about it. Same with the law. But with art, and old Jane or Joe can weigh in. I mean--your kid can do "art" by gluing macaroni onto a piece of craft paper! "Art" is crayons and watercolor paint, and Elmer's glue!