I don't want to "fix their face." Nobody's face needs "fixing." I'm trying to create the best photograph that I can, so I mostly make changes in light (or lack thereof) and color. Sure, some people have a blemish, I'll touch that up, but the moles on my chin? Those are part of my face! That's what I look like.
Like a lot of newbies, I've been guilty of learning a new editing trick and then overdoing it, spurred by the excitement and the novelty of the new power.
My general rule is 10%. Brighten eyes or teeth - but not more than 10%. Beyond that, it seems more artificial. It's not natural looking. Lightly touch up the highlights in someone's hair - 10%. Otherwise, you're making them look like people they aren't.
Sure, sometimes I go crazy, exploring new techniques and doing crazy things with colors - changing shirt colors just to see if I can do it, trying contouring and adding makeup to people's faces (same reason).
But, of course a photo for a client needs to be the way THEY want it to be. We talk our project ahead of time, explore the possibilities, clarify expectations. And that's when I can feel pretty confident (and edit more quickly) if I use the 10% rule.
Thanks for reading, and feel free to check out more of my work at http://elizabethmcquern.com/.