Don't forget to publicize your sale - I find the middle of the week before a weekend sale is perfect on craigslist. List your location (you can include a map), list directions and hours. And on craigslist you can be chatty - mention you're downsizing, list potentially valuable or interesting stuff, offer a bargain table, and let them know whether dealers are welcome or not (I usually post that earlybirds are welcome, but I won't give my best deal before published hours.) If you think you have something particularly sellable but bulky (furniture, perhaps?) you can place a separate ad for it on craigslist and include "email me or view at my yardsale at..." If you sell something before the yardsale, you can edit or delete reference to it once it's gone. Our local newspapers have started offering free online yardsale notices as well, but they're limited in size. Tell them what you'll do if it rains (I say "I can't deal with rain - I'll delete this and repost with a new time if rain threatens.")

If you can recruit neighbors to have sales at the same time (even within a mile apart in the country) you can publish together or mention each other and possibly increase traffic.

Clear signs from every direction are important. They can be handmade but have to be readable from a driving speed (ahead of a turn, perhaps).