I don't know that Garage Sales are a huge money maker, but here are my tips...
Make sure you have plenty of stuff - people don't want to stop at a sale with 4 boxes in the driveway.
Price everything - I know this sounds like a lot, but you can bulk price things to make it easier. "Everything in this box $1" or "Board Games $1"
Sort your items - people don't want to dig through a pile of clothes that include mens, maternity, and baby items all together. Sort boys from girls, and general sizes (Girls 0-18mo; Girls 24mo-3T). Make it manageable for shoppers to find what they're looking for.
Clean is best. No one wants your old boots with mud caked on the bottom. And if people see a couple of stained clothing items, they'll dismiss the whole group before they even check it out.
Friday and Saturday usually works best... not Sunday.
LOTS of big colorful signs. Only put them in the area between the sidewalk and private property. Signs put up in the median, or in the grassy area between the sidewalk and street often get picked up by the town. Make sure people can find your house based on signs from the make roads.
If you choose to advertise, use a local paper, like the Denton RC. Craigs list is a free option, too.
Make sure you have plenty of change (coins, singles, 5s, etc.) A good apron with pockets makes it easy to carry your change, and allows shoppers to know who to ask when they have a question.
Have lots of plastic bags (the kind you get at the grocery store) available, along with an extension cord and outlet, if people want to test an electronic item.
Good luck!
www.familyeguide.com Free guide to affordable family activities in Lewisville, Flower Mound, Highland Village, and the surrounding communities.