Wherever our stories are set, whatever our characters do for a living, we can follow the same advice by writing from our hearts and with our senses. But sometimes our stories demand more. Maybe it's specific knowledge of police procedure or custody law. Maybe it's some nitty gritty detail about cattle brands or burn medicine.
Historical writers can go to old diaries, portraits and letters to learn their subjects.
Some writers swear by the internet, where thousands of resources are a click of a mouse button away. In my case, unfortunately, it usually takes a heck of a lot of clicks to find the information I need. I didn't, but my insurance agent did. The emergency room director of the nearest hospital told me that. I didn't, but the assistant attorney general for NC set me straight.