It's ALL about the details. Really. If you know something's wrong just don't do it.
In a novel I wrote some years ago (not published) I created an entire world. I researched geography and weather patterns so deserts would appear on the correct side of mountains, lakes would form in the correct place. Dialects would appear based on shifting population changes, and so forth.
I know you don't all like AWMS but everyone who's read it is amazed at how real it feels for a fantasy novel. It's the details. If you ever go to London you will find everything where I say it is. Every ghost train station exists where I say it does, every date on the trains is right, all the details about Scotland Yard are right. If you visit the airport terminals (SFO, JFK, or LHR) you will find everything was where I said was down the correct decor for that time period. You will find pilot announcements are accurate for the time, and so on.
It's the details. Overkill I know, but still. If you CAN do it right, that's the way.
My two pence.