I LOVE yard sale season. I'm having one this Friday at my mama's house actually.
My #1 tip would be to ziploc small stuff. Buy the cheapie ziplocs from the dollar store in various sizes. Works for kids shoes, puzzles, hot wheel tracks, baby clothes, etc. It makes it easier to keep everything together and things in ziplocs for me sell better.
I hate fanny packs and my mama's doesn't quite fix around my waist, but they are very convenient when having a sale. Once I get a wad of money in my pocket, I give it to my mama b/c I have dropped bills a time or two. I also carry a pocket calculator, my brain gets tired of adding after a couple hours, lol. Also, have plenty of $1's and quarters. I price everything in quarter increments. For my kids clothes (my biggest seller) I sort them by gender, then size, then season in sections on a picnic table, then I refill from bins I've already organized on the ground. For clothes, I type a sign in list form for example: Boys sz 5, 6, 7- Coats $5, Jeans $2, Shorts $2, PJs $2, Shirts $1, Shoes $1 and tape to the front of the boys section. I have individually priced, but it takes forever or in my case 2 weeks.
Advertise for free on craigslist, yahoo groups, and facebook. Our local newspaper costs too much $$ IMO. Make your signs big and use black marker. I've passed too many signs written with pen that I couldn't read.
Have fun! Good luck!