DON’T skimp out on your drapery rod. Proportion your rod to your drapery. Drapes with substance that have pattern and colour and hang in a large window will take on a uniform look with a beefy, thicker rod. Ensure your rod is supported with the correct amount of brackets as to not allow bowing in the centre. (Bowing rods is another pet peeve of mine.)
Big windows, big rods. I believe you should use big rods for all windows, large or small. Use large, thick rods with interesting finials. (The decorative pieces at each end of the rods) This detail will act as jewelry in a room. Even if the drapes are never closed; a thicker rod acts as a bridge from one side drape to the other side drape completing the whole package. If you already have a smaller, skinnier rods and you want to use them, use them at smaller windows.