First, it'll be a separate room, in the hopes of keeping my work somewhat separated from the rest of my life. Of course, we know me, and we know how much my work likes to creep in, and how my work is actually one of my interests. However, the separate room is key here.
Then I'll have a desk--the corner desk I have now, in fact, or a similar desk. The desk will face away from the door in order to lessen the distractions. Compy will be on the desk, along with other trinkets. To my left will be bookshelves--all filled with books, dictionaries, and references. To my right will be a chalkboard for my math. I may paint some of the floor in the chalkboard paint for the days when I'm feeling childlike and just want to work on the floor.
There will also be another table and a comfortable chair or two on the other side of the room for those times when I get tired of the desk. If the office is too small, then the table can be behind the desk, I can just have the desk chair, and I can paint the table in chalkboard paint. The extra chalkboard, though, is essential.