Really, anything in the
Foundry Tutorial and Guides forum in a good place to start. Specifically, I'd look over at least these topics:
How to Make a Map
Suggested Map Making Tools
Mapmaker's Guide to the Galaxy (under construction)
A How To Guide: Giving and Receiving Feedback
Additionally, follow a couple of maps in the Foundry, and understand how the process works. Watch and be a participant before trying to actively create your own map. It'll help your success in the long run, surely.
Those will all give you a good place to start.

Good luck!
--Andy