DMs of #dnd, what is some advice for those who want to develop more detail in their world? If you have general social structure, themes, the framework of a setting sorted, how do you fill in details?

One thing that I have found is that whenever I have taken the time to plan out a general roadmap, my players never follow it. So I always just let the players take a look at the map decide where they want to go and base the story around that. It won't work for every group but it works for us so far.