It used to be that I had to have music on. Like soundtracks and such would really get me motivated. But now, it turns out that I need absolute silence to write. The only time I listen to music is whenever someone is being loud in the house and kills the sanctity of silence, so I blast my iPod in return. With headphones on, of course.
I also find that I can't write well in the morning. It's weird. Maybe it's because I'm groggy or something. As for the mood, I have to be calm. If I'm angry or sad or something, I can't write. My mind is focused on too many things then.