I recommend the "real world photoshop book" I have the CS2 version and it is great!! I now have CS4 and still am able to use everything I learned in the book. It will teach you how to do a lot of stuff in photoshop. The book walks you through bad images and how the audthors used photoshop to make them better. The authors focus on one aspect of editing at a time, so you can flip through and find an area you would like to learn. I would recommend you start from the beginning, read the book to the end, and play around with photoshop as you read. The book also discusses printer profiles, color mgmt, shortcuts and much much more. It is almost 1000 pages long, but you can work through it. I started reading it when I had free time and learned alot. I can now produce good photos very quickly. It will take some time to learn but it's really worth it. Hope that helps, let me know if you have any questions, I can share my experiences.
James