If it rains and you have the sale in a part of the house or garage control where people are going. Rope off where they are not supposed to go.
If you have things that are more valuable have someone stand over them to watch they don't just disappear into someone's pocket.
Have plenty of change both small bills and coins. You would be amazed how many people show up with $20 bills to buy something for 25 cents.
Save your plastic shopping bags so you can put sold items in a bag for people to carry home.
Have old newspapers to wrap fragile items for people to take home
Have plenty of help throughout the day. Being alone with 10 people in the yard and needed to go to the bathroom is a real pain
Have some sandwiches or easy eating foods handy. If you are busy you won't have time to go in and make something - same for drinks.
Have something outside for you to sit on for those quiet spells.
Advertize. If legal put up signs on posts, in grocery stores/pharmacies (wherever they have a board you can post signs on) - even the newspaper.
Place a sign also at each end of your street to direct people to your place
Place some balloons out near the street so people coming down the street can easily see where you are.
If you can place items on tables so people don't have to get down to the ground. Arrange the tables in a way to control the traffic flow if a lot of people arrive at the same time. You may find it easier if THEY are on one side of the tables and you on the other side. But if you have alot of stuff then you might need to arrange it so people can wander on both sides.
If your yard is enclosed have your "check-out" near the gate so people have to pass you on the way out.
NEVER EVER leave the money alone. Carry it on you. I find a tool belt with pockets was great, separating the coins into different pockets
Smile and have fun, joke around, have some fun music playing. Don't ignore people but don't pester or hover either.
The idea of putting similar priced items on a table with one sign is interesting and do-able as long as things don't travel from the $10.00 table to the 10 cent table. For this to work you would need to be watching or have someone at each table if more than one.
If you don't have enough tables get large boxes. You can turn them upside down and use for a table or just throw a lot of unbreakable things into the box. Some people enjoy rooting through things
I will come back if I think of anything else