Have a writing room. It should be a humble room.
This comes from Stephen King. He says that during his amateur years, he imagined having a ginormous T. Rex desk that he could write in. It was placed in an addition to the house, a converted garage. No more days of a student's desk in the laundry room of a trailer. No more writing at lunch at the mill. These were also his drinking days, where his garbage was filled with bloody coke spoons and cans of Miller Lite.
Once he got sober, he changed this room into a second living room, and traded in his desk for one half its size, and fit it under the eave in the corner.
I don't really have a writing room. I think that you should be able to write anywhere. The environment (as long as its not distracting) should not have an effect on the mind, just as substance abuse doesn't have an effect on your ability to write. I first wrote in bed, before I went to sleep, and had the room quiet. That was when I wrote on paper. Then when I went to college, I gradually transitioned to composing on the computer, once I got my own (and in my mind, I thought, "I'll never be able to compose on the computer, that's just not what I do, it's not how I'm imprinted!"). Now I do all my writing on a computer, and can't go back to pencil and pen. It's just too slow for me. So I guess you could say, my room is the computer. As long as I've got one, I feel comfortable enough to write. And I guess that's the point. Just so you don't get into this case: