I try to do as much as possible in the camera so I don't have to do anything in Photoshop. Framing, exposure, depth of field are all things that should be considered BEFORE you push the button, not after. My general rule is that if you have to spend more than 10 minutes fixing a picture, it's not worth it.
Having said that, here are some neat little tricks for images that aren't quite where you want them to be...
Framing:
Look at this for example. On the surface it's a decent enough picture.
However, it suffers from a few fatal flaws because I didn't consider framing it. The tree growing out of the back seat is the major killer. The tilted angle is bad and the sign and buildings behind it distract from the thing you really want people to look at, which is the car.
A more appropriate example would be this:
The level horizon and lack of distractions in the background help people to focus a lot on the real subject, which is the car. I'm not crazy about the trees on the hood, but that is minor compared to what it was and is easily fixed in a couple of minutes in Photoshop.
To be continued...