It seems that I still have a lot to learn about lighting. And if I had the opportunity and lived in a location to get some education about this, I definitely would. So I'm writing this for others that are in a similar boat (here's an oar).
I go over my rejections very carefully to see what I might have missed when I decided to upload that certain picture. 9 times out of 10 I find that bit of the photo that just came out poor and learn what to look for in the future before I decide to upload. (It's that one that gets me to think I might need an education.)
Normally what I find is pixelation in one area of the photo (which would be caused by poor lighting or improper exposure) or it has distracting shadows. And this link is very helpful.
So what I've learned so far is this (this list is more for myself to keep reminding me until it becomes second nature. But I thought it might help a person or two)
1: Get as much light on your subject as you can. Here's another blog that is helpful. If you're outside, use reflectors (like a sheet of paper or cardboard wrapped with tinfoil). Inside, do whatever it takes to limit distracting shadows. And it's usually in the shadows that I find issues after processing.
2: Inspect your image at 100% and look over the entire picture.
3: If you're adjusting your picture (lightening/darkening, color enhancement, etc) make sure you go over it again.
4: If you get rejected, go over it again and try to figure out why for future shots.