It pretty much depends on what you want to use it for.
For this one, I got started with
- dividing the different races and what their environments in general would be (forest, valley etc...)
- focus on fundamental/important points first and go to details from that
- don't try to think about the geometry as much - nature isn't linear, so you don't have to dwell on the "perfect form"
(you could use some tools for that as well to get some cool shapes - like scatter cornflakes on a piece of paper and draw a line around them or something)
- also I tried not to "overload" the map with information, so it can be easily understood
- last but not least - don't rush - take your time with details and such until your satisfied
Hope this helps (I'm no expert though, I just worked on it till I liked it )