Sam, I tried a quick one for you.
Good retouching is like being a good doctor. The diagnosis is the most important thing.
Ask yourself first: what is wrong with this image? Is it to dark, to light, to much contrast or to flat, over saturated, not enough saturation, "wrong" colors in skin tones, to noisy, out of focus.
Most important is to start the retouching of a foto in the following order:
1. Curves, Check and adjust the highlight (3%), check and adjust the black (96%), then lighten or darken the mid tones by pulling or pushing the curve in the middle of the curve.
2. Color correction.
3. Hue and saturation.
4. Retouch skintones (blemishes) with a small but soft brush. Zoom your image to a 100% on your screen for that. (Beauty retouching is a different story).
5. Reduce noise if necessary, (Topaz deNoise is one of many tools).
6. Sharpen image if necessary with unsharp masking. (Set Radius to 0.5 pixel).
Since 1970 I worked in printing business as a professional retoucher, and since 1994 with Photoshop. These many years of experience are hard to put into a few sentences. Though I really hope that I can help you to improve the quality of your pictures.