I'm doing an adaptation of a novel, and I want the first shot to be a black screen with a voice over of a little girl, and then a slow fade in. How exactly would I format that?

Technically the decision to slow fade or pan or cut to is the director's decision, not the writer's. That said... here's the opening of "Crash", which starts in black. And if it's good enough for Paul Haggis...

"OVER BLACK we hear the sound of a violent rear end COLLISION, brakes locking, metal crunching, tires skidding as a car spins, horns blaring, gravel spitting. Then silence. We start to glimpse faint, unfocused images of flashing lights.
Superimpose: Tomorrow.

GRAHAM (V.O.)
It's the sense of touch.

RIA (V.O.)
...What?

GRAHAM (V.O.)
Any real city, you walk, you're bumped, you brush past people. In LA, no-one touches you..."

Or, more simply, the opening of "Get Shorty"
"BLACK
MAN'S VOICE
Looks fuckin' cold out there."

-------------

SF08: Gethsemane (working title) - Thriller
SF08: Shooting - Comedy

Good luck to you all.

Okay thank you!

Actually, as a writer you do have a choice on how you start it. Instead of starting like this:

FADE IN:

Blahblahblah.

You would do this:

BLANK SCREEN:

VOICE (V.O.)
Blahblahblahblah

FADE IN:

Blahblahblahblahblah