How do you do proper multi-location SEO?

There is a lot of outdated and misleading information out there about how to do a multi-location SEO strategy. Questions like, Do i need local numbers? Can i use a home office? Do i need services area pages or a website? I find different answers all the time, and i can't, in good faith, sell a multi-location strategy when i don't know what will work best.

Does anyone have a guide, or know best practices?