Position this near the center of your garage sale so people will then see what else you have out. Make sure you have some items outside of your garage to catch people's eyes as they drive by. Bicycles, baby items, furniture, etc. Some families put up balloons or banners to get cars to stop and look. If everything is hidden inside your garage, it may be difficult for people to see what you have, and they may pass by without stopping.
People love to dig through boxes looking for hidden treasures.
You can make a good side profit by offering coke, juice boxes and snack items like donuts and chips for 50 cents each. Many shoppers will be hungry from getting up early, and parents will usually buy their kids a snack just to keep them quiet and happy for a little while longer. Finally, be sure to have at least two people manning your garage sale. One person should be available to answer questions and walk around, the other to ring up sales. You may not need both people at all times but it will help tremendously to be able to walk over and answer questions without leaving your jewelry and cash unsupervised.