Who doesn't want to do things on the cheap sometimes (read: most of the time). Getting a garage sale happening in your own back yard (or garage, front yard, pavement, mates house) is so cheap it can actually make you money! A garage sale is a social, spring cleaning Saturday in my book.
Step numero uno: Go through all your stuff, yes…all of it, and have a good think about what you need and what you don't. From books, clothes, shoes, art, plants, homewares, kittens someone is surely going to want it! If you have housemates, get them involved, or get your mates together to contribute stuff for the sale and to help you man the stall. Furthermore, ensure your mates come round to keep you company but also act as rent-a-crowd...after all, people attract people.
Great ways of drumming up publicity for this is to create a catchy Facebook event in the week or two leading up to it (make it public and appealing). In the couple of days leading up to it a few posters never go astray, and often your local café will be more than happy to put them up for you as well. On the G-Day (Garage-sale day, stay with me here), grab some fat sidewalk chalk and grab peoples attention. Short and sharp – arrows are good, people love following arrows. These can be placed in areas near local shops, café's or markets. There are online and print options for you to advertise garage sales too, but that is putting some money in, and this article is about cheap cheap cheap (although the argument here is that it will create more publicity and interest in the event). So I'll keep this decision up to you.
On the day you need to look after yourself. Do this by ensuring you have food and refreshments handy, chairs (comfy, as it can be a long day), friends to keep you sane. For the buyers you'll want any or all of the following – display table, clothes rack with clothing hung up, a $5 bin, a mirror. If you are feeling uber domestic it is a cute and appealing idea to cook some muffins, banana bread, or gingerbread men to flog (or giveaway) on the day. NB: some people will want to know exactly what is in them, so it is an idea to keep the recipe close.