Make sure you put price tags on everything or else people are going to be walking up to you constantly asking how much it is. Don't price tems high. Trust me, unless they're super expensive items in high dempand, they wonkt sale. Be friendly. Word of mouth spreads fast exspecially if its a small neighborhood and you plan on having other yardsales. Start early. They usually start between 6 and 7 in our area.
Make it easy on yourself. Keep in mind the goal is to get rid of the stuff. If you price things too high and aren't willing to lower lower lower the price you will have to repack it all and move it with you or take it to the salvation army. Who wants to do that? Also have a big FREE pile.
Price low and have it organized as best as you can.
One thing I hate about yard sales is, you get some who price their items as brand new store bought prices. Like clothes, I will find clothes that are marked 3 bucks to 5 bucks, well I always pass over those items because I am not paying 5 bucks for a used shirt for me or my kids. However, I will pay 1.00 or less for it. Just remember to price low, you want to get rid of items not get rich......
What everyone else has said is true. I've never had a sale myself but I am a seasoned, 3rd generation garage saler lol. People can tell what's valuable or not, so price things right. If it's only valuable to you, then don't price it too high. I've been to so many sales where somebody is emotionally attached to something so they price it higher than what it should. Shoppers can tell if you fall into one of two categories: person trying to get rid of stuff, or person trying to make money. If you do it right, you'll do both.