You may want to hold it on weekend, maybe Friday Saturday. Attendance depends on advertising, so put out the items, but keep the expensive stuff in the back. In fact, you may want to advertise some of the stuff on Craigslist or whatever.
You ll definitely get more traffic if you hold it on a weekend. Remember, people with money usually work on Thursday and Friday. Also, when you put a price on everything be sure that it is at least 5% higher than what you want. People will not pay the price that is marked they will want to get a bargain. Also, some of this stuff will sell way quicker on Craigs List than at a garage sale. Like the baseball cards. That is a niche and it s not likely that you ll get the money they are worth selling them at a garage sale.
Make sure you have a BIG sign, and have signs to match posted at every turn from the nearest major road... (Make them visible and high-contrast, but still eye-catching, like HOT PINK with thick black words or something)
