The best listings include several well-lit photos of the actual item you're selling (again, no stock photos), accurate measurements, and a detailed description that clearly explains as much as possible the condition, age, and history of the item. Also include the approximate location (zip code is sufficient) and options for pick-up. If you are able to deliver a large piece, call that out, too -- delivery is a huge plus, especially in urban areas. Finally, price your item appropriately. Most Craigslist buyers are looking for a deal, so as a rule, price used items at no more than 50% of retail. One exception is antique or vintage furniture, which often commands premium prices, especially for popular styles like midcentury modern (thanks, Mad Men).
Caveats: Let's face it -- inviting a total stranger to your home is kind of creepy. Though I've never had a problem in many years of using Craigslist, you don't want to take chances. I try never to be home alone when someone comes by, and for smaller items, I'll often ask buyers to meet in the lobby of my office. Also, reduce the risk of scammers by only accepting cash.