This could be considered a followup to this post.
A surprising number of new photographers seem to be unable to see things like contrast or saturation. They seem to be able to tell when their image isn't very good, and they certainly like it when someone increases the saturation or whatever, but they don't seem to see what's missing, in any particular detail.
I do, generally, and I dare say you do as well. Still, here's a handy little test chart of the sort (right down to the somewhat crummy photograph used as a basis!) that appears in every How To Take Pictures Book ever. Do you see what's going on in each row? You can, I assume, see that the three images in each row differ. If you can't see how they differ, look more. It'll be educational!
This image is now public domain. I made it, I say it is so. No rights reserved.