World Building: Where Should You Start?

I’d wager that every GM of at least a few months of experience has either considered “world building” or done it. It seems like a massive, maybe daunting challenge, and it can be. Where, then, should you start? Herein we begin our extended series on world building:What size should you make your new world?And by "world," what do you mean?How to think about which system to useWhere to find inspirationWhen to start "building