I can't say enough about this column by Steven Savage. It is jam packed with great advice and tips for worldbuilders. Whether you're new to it or have been at it for a while, it's a must. Sadly it has been defunct for some time now, but a big thank you to Seventh Sanctum.com for hosting such a wonderful compendium on top of an already great generator.
Without further ado, have at it:
A Way With Worlds