If you are in a major population area that has a Craig's List, that's been way better for us to sell ATV and dirtbike parts than newspaper for sure. When it comes to selling a whole bike we do list on Craig's list, but have had best luck with ATV Trader (print and online). Also suggest you find an active dirtbike bulletin board for your region or state - Most of those postings are free or pretty cheap.
Whatever your choice, pick something that's regional so you aren't messing with shipping the bike, scam money orders, etc.