Exactly what others have said.
Price things, -think to yourself, what would you be willing to pay?
Organize is the key. Usually the week of the sale, I start bringing everything into our front room and start pricing and putting things in to like catagories. Much easier to look at all the baby stuff, and all the computer stuff, etc in one area.
The night before, bring up all tnales etc into the garage and get as much as possible on the tables to be ready to go.
Put BIG items out in the driveway- this really draws attention to your sale.
Have a "free box" of old McD's toys, small pieces of stuff for little ones to play with, and even take one home. Parents will stay longer if the kids are happy.
Be prepared for early birds. try to have as much as possible done the night before- no fun trying to still bring things out of the house when you have people mulling about- you just never know what they are up to.
You may even want to have a sandwiched made for you to just go in and grab quickly during a lull- unless you have a friend or someone else at home to help out.
Plan on eating out that night. Or fire up your crockpot!
Expect people to haggle- don't do it too early on in the sale- unless you really just want to get rid of the stuff.
When all is said and done, load up the car and drive right to goodwill and make a donation of the things that didn't sell
Have fun and good luck!