There was a very interesting post over at Laura Stanfill's blog (I've used that phrase before, I know), called "Prostitution, Or Writing What I Don’t Know." The subject was writing things (people, places, times) that you don't know from experience.
As with some other really good blog posts, the comments (26 so far) expanded on the subject and also went off in some other interesting directions (Angela's Ashes, the New York Times, writing to an outline, blocking the internet to concentrate, and others).
One additional point occurred to me, which is that you can leverage the things you do know to bring the readers through the things you don't. For example, why are the monsters and other special effects in the Lord of the Rings movies more convincing than those in the later Star Wars movies? Partly because of all those incredible shots of the (obviously) real hills and mountains and plains. When the monsters appear, you're already accepting what you're seeing as real (since so much of what you've been looking at was real). In the Star Wars movies, everything is fake, so none of it is very convincing.
This is important for mystery writers in particular because, as far as I know, very few mystery writers have ever murdered anybody (of course, and this is an important point, this is true of almost all mystery readers as well). But if you establish the setting and the characters well, by the time you get to the murder you've got the reader on your side (in business-speak, you've got their "buy-in").
Here's an example. This is from "Live Through This," the eighth chapter of my novel U-town. The setting and the events are things that I'm very familiar with, which I hope carries the reader through the parts that are not like anything I've ever experienced.
The Band (Kingdom Come):
Henshaw (guitar, vocals, songs)
Pete (bass guitar)
Carl (drums and lyrics)
CJ (fill-in lead guitarist, a gang member)
Jenny (Henshaw's girlfriend)
starling (Pete's friend, a killer)
Daphne (Carl's dog)
This post is somewhat of a sequel to my earlier post "What You Know."