My mentor taught me a way which I think is quite effective - start with fully manual camera with a 50mm f1.8 lens and produce standard 6x4 prints processed with no manipulation. When you can take a picture in most circumstances which is exposed correctly, composed correctly and is a final product..... then you may use zoom lenses and cropping as you know why you are doing it.
Quite a good logic I think as you're going to get the "best" quality image from a full frame enlargement, rather than a sub-crop enlarged by a greater magnification. Therefore it's desirable to get it perfect in-camera, but by no means unacceptable to produce a final product which has used techniques like cropping to improve it further.
Rob