Do you prefer a particular decorating style? What degree of formality do you want to achieve?
How much privacy do you require? Would a top-down/bottom-up treatment be beneficial?
Do you have gorgeous views you'd like to see while still protecting your floors and furnishings from the sun?
How much light control do you want. Do you need total darkness to sleep well?
What directions do your windows face? Is the control of heat and glare an issue? Do you need coverage for the cold?
Are there any interfering factors such as window cranks, crown moldings or beams? Is the window located in the corner of the room so the extension of the treatment may be effected?