Have you ever checked out our Archive?
http://wayofthepixel.net/index.php?topic=2076.msg161933#msg161933If you already know how to set up photoshop, the rest comes from your drawing skills and practice.
While there are a multitude of tutorials out there which focus on specific techniques, like tiling, AA or how to Dither, it's pretty hard to find good stuff which goes step by step over everything - because it's complex and there are tons of different styles.
But in our archive you can see threads from people of all skill levels, their problems, and how they solved problems according to their critique.
Is that what you are looking for or is it too advanced?