This tut will hopefully stop newer mappers from making world maps that look something like this:
With world maps, you need random and varied landscapes, cliffs (most people don't bother with them, but they look awesome), and cities placed where cities would really be placed. I'm gonna start this one with a lot of water and several amorphous blobs of grass and snow. The circle and pencil tools are both important here. You can either make an outline of your landscape with the pencil, then fill in the rest when you're finished, or you can quickly draw ovals on top of one another until it forms something asymmetrical.
Of course, this is just for demonstration. I'm doing it fairly quickly, but you should take your time setting it up. After all, your group is going to be traveling around it for a while. As a side note, make sure you're using the real snow tools when making your snowy areas.
After you get that done, it's time for mountains, trees, and cliffs. I'll start off with a little piece of the map that I added a cliff to.
Oh, and right now I'll apologize for my somewhat sloppy mapping (I can spot a couple mistakes in that one, ugh.), but at this point I'm just hoping to get the concept across. Anyway, you can see how the difference in height adds a whole new dynamic to the map. If you're feeling really gutsy, you can maybe even put a castle at the top of a couple layers of these. As for the rest of the map, keep it occupied, but not cluttered. Use forests and mountains to cover up dry areas, and most importantly, keep it all random.
Wow, I'm starting to get insanely lazy
MAPPING TIP OF THE DAY: Finish your cliffs (Use mine as an example of how -not- to finish your cliffs)
There isn't really much more to it. Utilize all types of terrain, get creative with it, and be patient. Good mapping comes from having attention to detail and the constant doctoring of your maps. If you see something wrong, change it. Do that, and your world map will turn out just fine.
^^ I'm most likely going to revisit that map. It probably isn't the best putting out a half-done map for a mapping tutorial, but I'm currently pressed for time and I have a feeling that a couple people wanted something at least somewhat close to this.
EDIT: One more tip, doing this will cover up land surrounding your cliffs: