I agree with Skip. The thing is, it's a continuous scale, so you don't just get to a certain point and become a good photographer. We're all learning all the time. Most of us on this forum would be considered a good photographer by our friends, but we'd also be well aware of others who are much better than we are.
Much of it, at least early on, comes from attention to detail, for example noticing things in the frame that might detract from the final image, so cropping them out, or hiding them behind another element, or maybe changing the angle. Similarly, understanding what the light is doing in the image, so you don't unintentionally bleach important elements, or lose them in shadows. Composition is a key part. Often you can transform an image just by changing shooting position a little.
Obviously the technical side needs mastering, so you know when to use which lens, aperture, shutter speed, etc. That's just knowing your tools.
The greats have wonderful imagination and can bring elements together that most people wouldn't think of. This is where I personally fall short - I would call myself a "proficient photographer" - and if you wanted images to illustrate an encyclopedia I could provide them all day long. But for shots that blow you away, I would struggle to construct something from my imagination.
Mark.