It's not always easy to use the dodge/burn tools and get it right the first time. If you see the error immediately you simply undo. If you don't see it until several steps down the road, the history palette is your only hope, but that can be a pain if it means reverting several steps.
- create a new layer on top of the layer that you want to retouch
- set the blending mode of this layer to overlay
- go to edit/fill... and fill the layer with 50% grey
- now you're able to use the doge/burn tools on this layer without destroying the original. Another positive aspect: using multiple dodge and burn at the same spot isn't going to harm the quality.[/list:u]
My advice is always: never do retouch work on the original. Use adjustment layers, masks, channels, blended layers etc. This way it's easier to undo some adjustments in a later stage. This will cost you some extra memory, but hey, we can't have it all