Three pieces of advice:
Post a picture if you can. Reduces random people coming to your house then complaining its not as nice as you described (even if you write "complete piece of shit couch")
Make sure to specify that the person is completely responsible for hauling the thing away by themselves (i.e. "bring a friend and a truck")
Charge some nominal fee. People are disbelieving of something free. If it's just really cheap, they'll love it. If it's free, they'll call up a week later and bitch about how it smells of desperate spinsterhood.
