I know different writers have different places they like to write. Some write at home while some prefer places such as coffee shops (J.K. Rowling, for example).
Me? I do virtually all of my writing while sitting on my bed. I've read in lots of different places that doing things other than sleeping on your bed causes insomnia because your head no longer associates the bed as a place just for sleeping. In spite of this, I still use my bed to read, write, etc. This is mainly because my room is the only place in the house I can go that's quiet, and I'm not a person who can write when things are going on around me. The only places to sit in my room are the bed and a very uncomforable wooden desk chair. Obviously, I prefer the bed.
Most of my writing is done in the evening and/or at night. While I will sometimes write at random points during the day, I always try and write for a while right after I get out of the shower at night. I don't really know why I chose that time of day, but it works for me. I'm a night person, and that's when I feel most awake. (Maybe it's because of the insomnia caused by using my bed for things other than sleeping.) I've been trying to write more in the afternoons, but it hasn't been working too well. I think there's too much going on, and I get distracted a lot more.
I'm always impressed that there are people who can write in busy places or as soon as they wake up. Those are things I wish I could do, but as of yet, have been unsuccessful. I'm someone who needs a nice quiet area where I can focus, and I'm definitely not enough of a morning person to successfully write right after waking up.