Retouching rock photography is a fun yet surprisingly subtle process that relies heavily on fundamental techniques.
Nearly every artist or designer will, at some point in his or her career, contribute something, in some form, to the creative juggernaut that is the music industry. Album covers, tour posters, promotional flyers, merchandise, magazine shoots - the variety of work generated by the industry is surpassed only by how many bands there seem to be in the post-MySpace world.
One of the completely unavoidable problems that most designers will run into when working with bands is that the photos supplied as part of the aforementioned assets will almost invariably be poor quality. If the band doesn't have a label with access to a full-service creative studio (which is probable, given that they're outsourcing the design or art direction to you!) the photography tends to be a fairly non-epic set of generic poses with poor lighting and bad hair.
Fortunately, much of this can be corrected quite easily in Photoshop using a few fundamental techniques and a little bit of intuition. Combine this with an Adjustment Layer or two and you'll end up with a classic rock feel that doesn't smack of obvious retouching.