I need to buy some dedicated electric shavers...
But in the meantime, I've just used manual shavers. I've cut with scissors prior in the past, but it's not necessary. Even if you have tons of hair down there, it doesn't hurt less or more if you cut with scissors prior.
Obviously, you want to be careful. It's really just the same as your face. Put hot water on it (opens the pores, makes the hair easier to cut, etc.). Try to stretch the skin where possible. Shave with the grain where possible (with the direction of how the hair appears to naturally grow toward).
My big tip (no pun intended) is to do it 1 or 2 weeks before the "big day" if you shave rarely -- especially if it's your first time. It's going to look weird, and you'll more than likely mess up in spots. But after it grows back a little, it'll look more natural and suave.
Ultimately, it doesn't *really* matter, unless she's going to be giving you a blowjob. I've also experimented in using it as a mental tool ("dress to impress").