Retouching is declarative, it is an assertion about the nature and purposes of the things to be seen in a picture. It is linguistic: it is about putting words to things seen in photos, and then forcing 'that which has been named' to conform to expectations. Thus, to begin retouching, one must invoke some standard by which a conceptualized artifact within a picture is judged defective. Retouching is discursive: it tends toward digression and distraction from the use of the picture. It is prone to jive and banter, to a repetition of form, to habits of treatment, which obliterate the subject. At its worst, it removes all the elements which are unique, engaging, and fascinating in a photo.
Fortunately, retouching is the least of what I do. Mostly I try to help the timing of the eye through the image with respect to the intent of the photographer and the use of the picture. Or I try to help create continuity in a story. I do this the way it was done in the darkroom, by large and small burns and dodges, by getting the color and contrast right, by consulting the photographer, listening, and by offering options.
I'm not above using any tool, however, I rarely use the clone or healing brushes except to remove dirt. Both of these replace what's-wrong with what's-right by moving pixels. I prefer to refine what's there. It looks more natural and photographic. And for me it goes much faster.
In a sense, each photo a unique waveform. Different frequency ranges correspond our feelings about detail, pattern, and overall punch of the image. Although the wholesale alteration of these specific ranges is almost always offensive, previewing the the image with these ranges in isolation makes it simple to refine any textural problem, which are mostly what people find distracting. Once I've isolated a range, it's also much easier to judge whether to do a lot, a little, or nothing at all. It takes longer to explain than it does to do.
My technique is to look, listen, think, and then do as little as necessary. Few pictures are the better after retouching, and the more done, generally the worse the result.