Take pictures (a lot of bad pictures if you're me) and find tutorials that might help. I have purchased books that have good tutorials. Most recently I purchased The Adobe Photoshop Cs3 Book For Digital Photographers by Scott Kelby. It's a good book and shows several excellent techniques for cleaning and improving images. It does expect some understanding of the program, but even if you're new to PS it will help. The internet is a great tool for finding information on how to use PS. A good link to look at is 100 wonderful photo effects Photoshop tutorials
. There is lot to look at there. You could also look at The Russel Brown Show
. Great site that covers a lot of different aspects of the PS suite, including action scripts you can download. Russel's tutorials are video based so I hope you have high speed. There is also a pod cast you can subscribe to. These are some of the places I found a lot to learn on, but there is more to find. Hope this helps.