1) Six degrees of separation. This is a good place to start. If you’re going to write about a murder in a hotel, your sister-in-law’s stylist will know the boyfriend of the night manager at a swank hotel—and you will get a great interview. Ask around.
2) Societies and Associations. A friend who wrote a novel set in the pioneering wild of early America contacted historical societies via email and received a wealth of information. Similarly, librarians are also experts in pointing you to the right shelf, especially at university libraries.
3) Shadow the real thing. If you can, try to shadow or interview a person doing the same job as your character. Remember people love to talk about themselves and welcome questions from writers—the idea of being a model for a character gives them pride in their career, however humble or exalted. Confess your ignorance and ask them for how things really happen.
*Information courtesy of Anthony Ehlers, author*