Well, the absolute best place to start, I think, is with Delgondahntelius' excellent description of his method: http://www.cartographersguild.com/tu...photoshop.html
My next best piece of advice is to look at lots of examples of the kinds of things you'd like to make. There is an excellent sticky thread in the Resources forum here with links to all kinds of historical maps to drool over. The Rumsfeld Collection is of particular note, since it's very deep and features images of decent resolution.
Some general study of the crafts of manual drafting and graphic design is also a good idea. You don't need to get deep into design, but I think it's helpful to have an understanding of the principles and elements of design, as well as at least a rudimentary understanding of both color theory and typography.
There are also quite a few resources on general presentation principles that apply equally well to both hand-drawn and digital cartography. I think it was either ravells or RobA who posted a terrific guide to label placement a couple of years ago.
Of course, as you have specific questions, never hesitate to ask them. There are many people here eager to help, and most of the time the advice is pretty good.