What I used to teach my university students is that a good photo is contingent on 2 major variables (in this order):
Without light, there is no photo. The direction of the light can also add to the mood of the subject. There are entire books written on lighting, but just practice this one thing: open your eyes and "see the light." Each scene or subject will require it's own lighting. What you want to say about that subject can be partially controlled by the lighting. Can light by itself be the subject? Absolutely. That's how critical is.
Most educators will tell you that you need to know the rules before you break them. Not sure I totally agree. Depends on the subject. A tilted or unbalanced composition can be just as effective as balanced. Basic composition starts with mentally creating a grid with 6 equal sections to the framed shot. Use those intersection points to control the composition. Look at EVERYTHING in the frame. Shoot it with a balanced composition and with an unbalanced composition. You'll find that each approach has it's own appeal.