My general rule is to look at the histogram and try to elevaluate if any clipping is occurring and adjust the exposure compensation accordingly. I don't generally delete these images as I like look at the properly when I get home so I can the difference between them. Just like you I'm still learning !!!!
I do delete any images that look blurred, if they look bad on the camera screen they will look awful on the computer. I zoom in as much as possible and I try to look at the detail to make sure I'm happy with it.
You can turn on the "Blinkies" which show you over exposed parts of your image, and also you set up the camera to show you which autofocus points achieved focus during the shot. That way you can tell if you managed to get your main subject in focus or not.
If you want to edit any of my images to demonstrate points/techniques to either myself or others please feel free to do so.
Still learning with Canon 40D, 28-135mm, 100-400mm L and Elements 6.
Any Advice greatfully received.