In 1975, Gary wrote an article for the newsletter Europa's April 1975 issue. In it he describes how to build a campaign world in 5 weeks. Ray Otus turned the 2 page article into a 40 page workbook that delves into each of the 5 steps.
Enjoy
Gary Gygax 75 Challenge
I didn't use this when I made Malignost. It's a good way for a new GM to design their first world.