Like most things, arranging a room is much easier when you have a plan. Especially when you are considering a furniture purchase - it's good to have an idea of how it will work spacially with your existing pieces. As Maxwell discusses in Apartment Therapy (the book) you want to be sure to keep the flow of the space in mind.
This nifty book/kit would be a fun way to approach the task. Design tips, budget worksheets, laminated grid pages and (best of all) 300 vinyl furniture stickers. Sounds like colorforms for grownup design fans!
The Space Planner - A Home Decorating Design Workbook by Meg Mateo Ilasco