Pick a weekend that will be nice out - nobody wants to go to yard sales during cold weather. Put a bunch of signs with the dates, address and time around the neighborhood. You can even advertise it in your local newspaper so people that don't live in the neighborhood will hear about it.
Also, make sure the signs are large with bold black letters. I've seen tons of signs that are the size of a piece of paper with writing that can't be seen while you're driving past the sign. Those yard sales get ignored by most people.