Probably one of the most useful Photoshop tools ever, the clone tool enables you to perform all kinds of magic on photographs. You can enhance skin tone, clone out that freak in the background of all your picnic pictures, or get rid of a color that clashes or a distracting element.
In the following layout, I used the clone tool (as well as some recoloring of the photo, and some different blending modes) to even out my nephew's skin around the eyes and the bridge of the nose, as well as get rid of all that teething drool. =) I find that the easiest way to work with the cloning tool for textured surfaces or non-detail work is to use the clone tool set to NON-aligned. Then, each time you pick up your pen, you go back to the same source point instead of picking up continuous pixels. This adds more randomness and avoids having the texture look fake. In addition, try reducing opacity and using soft, grungy brushes that will also introduce a non-repetitive factor, which is pretty easy for the eye to pick up on. Here's the layout, followed by the pic (please click on layout for materials source (all Designer Digitals):
And here, just for fun, is a quick layout for a great picture of Candice (owner of Art Neko and Kathy (owner of Rubber Stamp Ave.) goofing around before dinner (the best crispy eggplant EVER at Fujin's, in Portland OR). Click on photo for details: