What is the best way to create a fixed subtheme with a narrow layout with 960px?

Right now what I do is moving the layout order

1-WIDE LAYOUT with: all and (min-width: 960px)

2- NARROW LAYOUT: With default values

3-NORMAL LAYOUT: With default values

but i dont know if this is right. I want to know if this is the only option and if im limited my options.