First point of advice would be to look at the Tutorial forum. Ooddles and Ooooddles of PS tutorials there, but also take a look at the Gimp tuts. Gimp is a free program similar to Photoshop and while not exactly the same, many of the functions are. Some people even use both to fill the holes in their preferred prog.
Second point would be to post a WIP (Work in Progress) early in the map creation process and update it as often as you work on it. We are quite friendly for the most part and will offer constructive c & c that will have you making wonders in no time.
And welcome to the CG