I have a good enough grasp of the character's voice that I don't do an exact script, just a hard outline(when I do have an exact script, my panelling gets shot to hell, because I have trouble visualizing per-page when it's in script format). I do thumbnails, trying to get as much that's being expressed into body language and say what can't be done silently through dialogue. I usually have a clear idea of what the conversation is, I just have to whittle it down to where it's not huge blocks of text.