Have lots of extra dollars on hand. Be sure to start set-up at least one and a half hrs ealy so you are ready for the first coustomer. Def have as many tables as possible to set out your items. Try to arrange them by the items that are alike.
Clothes will sell (esp kids) if they are dispplayed on hangers or layed nicly on tables in sets and arranged by season and size. I had a sale 3 weeks ago and made $250 on Fri only and mainly had only clothes. We had very little left for the next day so we donated the rest. You need to watch people b/c I have had people steal from me.
Also dont take checks or bills over $20.00 for your own saftey. If they want something bad enough there is always a corner store to get change at. Also for the people who want you to hold an item so they can go get money tell them you will for 1 hr and if they arent back then you can put it back out so you will be sure to sell it.
Be set on your price b/c people will try to get something for nothing nad thats not fair for you. I normally do jeans $2 shirts $1, shoes (esp if they look new still) $3-4, kids sets $3 and individuals for kids .50 or $1 if in perfect shape.
Keep in mind that most garage sale shoppers are also resale shoppers and know how much they sell items for there. That is how I set my prices and I think they are super reasonable.
Well I hope this helps a little. Good Luck w/ your sale.