It would depend on what kind of style you're aiming for with your map(s). If you want something verging on photorealistic, you could try Ascension's great Atlas Style tutorial, here cleaned up and slightly modified by Kindari: Atlas Style

Or the amazing Saderan Tutorial, by Tear: Saderan

If you want something more hand-drawn looking, try out Gidde's tutorial: Gidde's tut