So far, this is the best resource I've found on worldbuilding. I even like it better in that regard than the D&D 5e DM Guide, which is also a decent source. Berin has collected a good checklist of all the elements you need to consider when designing a scifi/fantasy setting. He provides some guidance about how to approach each element, and he stresses some good general principles, like how each element should be considered in terms of how it can create or resolve conflict in the story. I found this book really helpful. Thanks Berin!
[5 of 5 Stars!]