No music, no TV. BF and I both have our computers in the same room, so there's often somebody else around, but it goes better when I'm home alone. I can't write at work. Turn off the ringer on the phone.
Oddly enough, I write better when my moods are midline. Too happy, I want to be doing something else. Though, to tell you the truth, I had the best run of writing ever while recovering from a rare bout of depression. Writing can give me a feeling of accomplishment that can counteract more negative feelings, though. There's nothing like finishing something, hitting "save," and thinking "I so nailed that one."
I'm more of a morning person, so I save my heavy writing for weekends. I can't be hungry or distracted by pain or fever, either, it seems, but I need frequent 5-minute breaks, as in two to four times an hour! Weather doesn't have much effect on my writing, but time available does. If I have all day, I'll do better than if I have only a few hours.
I don't always know where the inspiration comes from. Usually, memory, but not necessarily personal experience. Something I read, or heard, or saw might bob to the surface years later. When memory fails, I make it up.