Location, location. location. Certain neighborhoods in the San Diego area are much better areas for garage sales than others.
I lived in one neighborhood that was a very hot garage sale area to find neat, fun, cool eclectic items. I found a number of great garage sales while living in this area.
I held a garage sale in this area of town and had a great response. There were tons of people who dropped by and looked at my things and I probably sold about $200.00 worth of random items that I was selling.
Later, I moved to another area of town that was closer to a lot of antique stores, so the draw to the garage sale was not as big of a success as the other location.
However, the thing that I learned from this 2nd Garage Sale was that the items that I photographed and placed on Craig's List drew the exact price that I was asking for-- rather than featuring them at a garage sale and having people try to run the price down to a minimum.
Craig's List can take a little bit more time-- because you are having to write a blurb about each piece that you are selling and photographing individual items, but you can retrieve a LOT more money-- if you do this over a period of several weeks, rather than an instant garage sale.
If you are going to hold a Garage Sale-- make sure to run an ad in Craig's List with the time of the event, otherwise, you will have people stopping by at 7 am trying to catch you before you open.
Leave yourself plenty of time--
If you are moving and wanting to clear garage sale items, then make sure that you hold this a month in advance. If there is rain/bad weather one weekend, then you can reschedule to another weekend.
Mark your items with stickers that have similar prices. This will help people find the prices that they want to stick to for their budget.