The amazing opportunity that window treatments offer is the chance to manipulate the architecture and mood of a room. You're basically placing a great deal of textile in a space — and well-placed drapes will work wonders.
1. The Fullness
Traditionally, you should be looking at 2 to 2½ times the width of the window for the fullness of the drapes. So if your window is 4 feet wide, the ungathered panels should be at least 8 feet wide, or even better, 10 feet.
2. The Length
For classic side panels, you really have to go all the way to the floor. If you're looking at ready-made drapes, make sure that they touch the floor, even if you have to buy the next size up and have them hemmed.
3. The Functionality
Oftentimes — and especially when privacy isn't an issue — we design drapes that really only function to frame the view. Even in these cases when the panels don't really need to close, they should at least look like they could close.
4. The Textile
There are never going to be any hard-set rules about choosing drapery fabrics. This is where design stops being a science and begins to be art. If your other furnishings are leaning towards solid colors, here's your chance to bring some pattern or at least a punch of color to the room.
5. The "Stack"
When drapes are opened, the space that the gathered textile takes up is called 'the stack.' You can manipulate the architecture by playing with the 'stack' placement If you're decorating a room with windows that feel too narrow, you can expand the fullness and visually expand the window by stacking almost everything to the outside of the window frame.
6. The Hardware
Much like the placement of the stack can expand a window, the placement of the hardware can also help a room. I always mount my drapery hardware as close to the ceiling as possible. Draperies will always establish the vertical mood of a space.
7. The Romans
Sometimes you just don't need all that fabric. So for kitchen and bathrooms, I often use roman shades. They can either be mounted inside the window molding, or outside the window frame. Whenever I use 'outside mounts,' I'll usually add a decorative valance over the window as well to balance things out.