A lot depends on how you as an individual learn but in general I would recommend starting with one of the many excellent books available, Scott Kelby's book comes to mind, but there are others as well. Since it is easy to become overwhelmed with all that Photoshop offers, concentrate on learning only the skills that you need and/or interested in, by following the tips and discussion in the book that you choose. Once you have an idea of what you are doing, determine if you need and or want additional help in which case, classes if you can afford them, and if conducted by a good instructor are great as are the various on-line tutorials.