Intruder, eh? To hide among us you'll need to fit in. I know: pick a likely style and fire up a tutorial. ;-). No better way to get helpful input than to post a WIP (work in progress) thread as you go through a tutorial, or as you experiment on your own.

So. What kind of story? That'll lead to what kind of map. Do the two of you have scads of ideas already afoot, or are you looking for an infusion of geography to kick start the imagination?