A garage sale is an excellent way to clear out the stuff you don't use or would otherwise waste money on for storage. Here are some great tips from "St. Louis Today."
(1.) Ditch the sale of clothes. Unless you are selling baby or kids clothes, all other items sell poorly. Perhaps you can make better money selling them at a consignment store.
(2.) Check out a few garage sales in your area to see how things are being priced. Also use brightly colored stickers when you price your goods.
(3.) Pick a date and time and advertise well in advance. Wed, Fri and Sat starts at 7am seem to be the norm. Don't advertise a closing time.
(4.) Clean your garage and groom your yard. Houses with curb appeal tend to draw more buyers.
(5.) Set up for your sale the night before.
(6.) Prepare for early birds (1-2 hr early arrivers) or advertise no early birds.
(7.) Everything is negotiable.
(8.) Take down your signs after closing and count the cash!
Read here for the actual article.
My experience with organizing my own garage sales is that a majority of items sell in the first hour. Sales after the 2 hour point are few and far between.