Organizing Garage Sale Merchandise
Organizing garage sale merchandise doesn't have to be all that complicated. There are a couple of very easy models that you can follow, or you can use something entirely different that works for you and your situation. Really, the key is to avoid making your shoppers work to find what they want. The easier it is for them to find it and know the price, the more sales you will make.
One simple way to get organized is to follow the example of larger department stores. If you have enough merchandise, you can set things up in "departments" to help your shoppers find what they want quickly and easily. You might have clothing on a rack or on tables. It might be wise to put these in plain view, but out of the way of heavy traffic so that browsers can check through what you've got without being nudged and bumped by people trying to get by them. This may seem like a small thing, but you want you shoppers to feel comfortable and not hurried.
For smaller, or more valuable items, it may be wise to arrange for them to be near a place where you will have a helper stationed. This doesn't mean that you need an armed guard, but if you are going to have someone manning a cashbox, you might place these items somewhere near them (but not blocking them). It is a sad fact that some people will actually stoop to the level of stealing from garage and yard sales. Even though the stuff might have been on the way to the Salvation Army after your sale, having it stolen from you just doesn't sit well.
Another option for organizing garage sale goods is to arrange them by price. This is a nice idea if you are looking to move many items at low prices. Laying out a $2 blanket covered with merchandise lets everyone know exactly how much the items cost. The downside of this is that you must remember where the items came from and where they started at the beginning of the sale. I suppose you could take a quick digital photo of the setup to help you keep track if your memory isn't serving you.

Consider keeping collectible items together.
Whatever you decide to do, remember that you should keep the shopping experience as easy as possible for shoppers. Many people will leave rather than search for items and for many experienced garage salers, a lack of pricing on merchandise will get them to move along immediately to the next sale, especially if it is a neighborhood sale where all they have to do is walk to the next yard. Take a few extra minutes to set things up right and you could end up getting a lot more of your garage sale items sold.