I run a huge charity yard sale every other year. We made over $1,300 last year.
For organizing, except for toys and furniture and other large items, have plenty of tables for displaying items, beg borrow and steal them if you have to. People are much more apt to buy stuff that they don't have to bend over or kneel on the ground to look at. Clothes, hang them, they sell better than those folded, plus people don't hesitate to step on them if they are on the ground. If you have a ton of stuff and don't want to price very single item, price by table and make sure signs are clearly visible. But even if pricing items by table try to make sure to group items of a similar nature together (craft supplies, dishes, decorations, sport equip, etc.).
I've learned that there are a number of unscrupulous people hitting yard sales. If an item is "real", i.e., Coach, Waterford, etc. make sure you label it as such on the price tag. Do research the prices that these types of items sell for on e-bay and craigslist beforehand and be prepared to justify your price but also be flexible. As a word to the wise, some not so nice people will try to switch the prices on these expensive items and if you have it labeled with the brand then you'll be able to say uh, uh sorry no that's not how that was priced as all my brand name items have price tags that say what the item is on them. And unfortunately, jewelry items, even costume, should be pinned to a board that is always in sight of someone. We had a few jewelry pieces just walk away before doing this.
Make sure to have plenty of shopping bags.
Change; have lots and lots of change, ones, fives and tens plus lots and lots of quarters.
Advertise, advertise, advertise. Put up signs, as many as your community will allow. Also advertise in the paper, both your community paper and the neighboring communities, place the ad the full week before hand. Also post a notice on facebook for your friends (ask them to spread the word) and list your sale on craigslist.
As we've learned to our regret, DO NOT hold your sale on a day that a big community event is being held unless your sale is right across the street from that event.
Our items are all donations, another thing I've learned: Even broken items will sell if priced correctly. We sold a broken (literally in 10 pieces) desk this year someone was willing to pay $10 for it.
For electrical items, have a really long extension cord handy so they can be plugged in to show they work. Have batteries handy to put in those items.
Line up places to take your leftovers before the sale. Best place we had to take our stuff, the local church was running a rummage sale at christmas time. They were very happy to take whatever we had.
ETA - if it is going to be hot that day or unbelievably sunny, make sure to have a shady spot to take items that could be destroyed by the heat/sun. Consider putting them in the garage or using a pop up awning if you don't have a garage.