I've always used word.
I've tried to write by hand some stuff but grow tired of it soon, my hand aches and it's slower than typing. I write by hand when is some short stuff like a small story or something, but screenplays always in word and when I'm already at a point where I feel is advanced enough I always send myself copies by email in case I lose my computer or something.
Never use index cards, but sometimes when I'm in the last part of the screenplay and wrapping up everything I make a list of scenes and then I might start moving them around.
I usually start with a vague idea of where I'm going and let the characters and their conversations kind of take the front seat and dictate the direction of the piece. Rewrites are mostly to get rid of stuff that stands out because it sucks one I reread it.
i try to let myself go in terms of plot, characters, vibe and, as leslie nielsen says in the naked gun: "like a blind man at an orgy, i have to feel my way through"...usually first instincts are correct, they just need some work done to them.
I also write where I can, but nights at home, completely alone and in silence are better.
I read this again today and boy, some things have changed. Since 2013 I think I've gone "pro", cowriting scripts with others which has forced me to quit using Word and start using both Celtx and Final Draft. I enjoy working on both, but FD is the one I prefer.
I've written three feature scripts since Psychotropic, all of them on Final Draft, and as far as my "lone" work is concerned, my process has not changed that much. All of those screenplays were not fully original; one was based on a story a friend told me (he never wrote it, he's not that kind of dude), the other one based on a chronicle another friend wrote about a weekend trip to Miami, and the third one is based on a magazine story by a respected journalist. Despite the fact that in all three cases I had some clarity about what the story was and how it was all going to end, I still just jumped right into it not really knowing the "how" and found my way as I went along. Rewrites have been sparse excepting the last one, which is a bigger and more complicated story, and it's a rarity because it has gotten longer in subsequent versions (usually is the opposite), I guess sometimes you need the extra pages.
I also cowrote (I am actually these days) two other features and in terms of cowriting it's been all by the book. Synopsis, long synopsis, treatment, save the cat structure, checking, character's descriptions, a lt of rewriting once you are scripting. It's interesting, but it's totally not as fun.
Also, I no longer wait for total silence for writing, cause then I would never do it.