Buy them a pizza with the profits. Saturdays are the best days for garage sales, but be sure to avoid holiday weekends. Make sure to set a rain date. The earlier the sale, the better. Bargain shoppers like to rise with the sun.
Garage is the obvious answer.
But, depending on the time of year, the basement may be a better idea. Be sure to check with local authorities about restrictions before announcing your sale. Also, be sure there is enough space for parking and people. Finally, publicize and promote. Contact your local paper about putting together a classified ad announcing the garage sale.