I'd say composition is the most important thing, because light, color, shapes, framing, are all parts of the composition. You can have the same elements, but put them indifferent order, and the composition and final result will be different or incoherent.
I suggest reading 'framed ink' 1 and 2 to learn a lot about composition, then you'll start to see things in photography, movies etc. That otherwise would be hard to even notice.
With this knowledge you'll be able to consciously read all images instead of just having vague feelings while looking at them
Piximperfect on youtube. If you follow his tutorials, little by little you'll get good at editing. It's the best channel for retouching imo