The resources suggested above are good ones.
In terms of approach, think about why you are world building, and what you want to get out of it. Do you like the idea of making up your own religions and pantheons? If so, do it. If not, get something off the shelf (like the book of the rightous).
Like working with the details, then do the details. Fill out that town, the surounding wildlands and countryside, and the local ruins/dungeon. Don't like that, get a big adventure that does it for you (there are lots if these floating around).
Maybe you like somethings about a published world but not others? Borrow what you like and change what you dont.
The reality is that world building can and should be a lot of fun. It is also time consuming, and there are a lot of resources that as a DM you can and should use if your time or interest is limited. And there are a lot of ways to go about it. But just step back and think, what do you want?