Here's a tip from my mom! I don't really like taking my curtains down to wash, but it's a good idea to do from time to time! Instead of washing them if they're just dusty and not dirty, try throwing them in the dryer on the 'air fluff' cycle with a damp towel.
My mom says that the towel must be damp for this to work.
This keeps the curtains from getting too worn or faded from washing them too often.