There are lots of books with lots of techniques. Also, there are web sites that try to explain one opinion or another.
When I first started shooting a DSLR, I simply shot a lot. I would try to post-process and "fix up" everything that I shot. Some I got right, and some I got wrong. I would print them up two on a sheet and show them to trusted friends for their opinions. Slowly, little by little, I got my eyeball calibrated to what others prefer. So, that had an effect on the degree that I attempt to "fix up" my shots.
If it gets to the point where somebody looks at it and says, "It looks like you Photoshopped this," then that means you are overdoing it.
---Bob Gross---