Selecting the right date is important so it won't conflict with holidays or special events that compete for attendance.
Weekends are generally more successful than weekdays.
Bigger is better. Practical household goods such as appliances, dishes, furniture, tools, and the like are good sellers. Clothing typically doesn't have a high resale value with the possible exceptions of children's clothing in good condition. Try to merchandise your goods in an attractive manner as if you were displaying them in a store. Items should be clean and if not in working order, labeled accordingly.