Well, 42, if you want some guidance the Tutorial part of the Forum is where you need to go. Be warned however, once there you may have a hard time leaving... Lots of VERY neat stuff there. You will notice that there are a LOT of Tuts for both Photoshop and the Gimp. I would stick to the Photoshop ones to begin with if that is what you are familiar with, but after you get comfortable with those I would strongly suggest looking at some of the Gimp ones. Both the Gimp and Photoshop have similar abilities and a tut for one often (with a bit of translation) works in the other.
If you have problems with finding a style, I would suggest looking through the Finished Maps and Cartographers Choice forums for a map you like the look of. Sometimes there will be a WIP (Work In Progress) thread where the techniques used to create the map can be found. Speaking of the WIPs, that is also a good place to pick up on how certain effects are arrived at.
Have fun browsing and enjoy the Trip
And welcome to the Guild, the Mappiest Place on the Web.