If you're posting to sell a local item for people to buy, make it as descriptive as possible and ad pictures when you can. You can add up to four.
Make sure you pay attention to Craigslist's guidelines about Western Union scams, etc. I've actually tried to sell a piece of furniture, and someone told me to send them my details to a certain address. They were going to have the moving truck come to me.
I was suspicious, so I asked the person to call me. A person interested in getting his furniture will definitely want to hook up with the seller. Nobody called.
If the stuff your selling is portable, try to meet in a public location like Starbucks or a book store. There are real goofballs on Craigslist that could do you harm. That's why I prefer eBay selling, even with all the fees.
If you're trying to promote a make money online program on Craigslist, you might as well forget it. Recently, Craigslist put up a huge warning in the jobs section about affiliate scams and recommends reporting affiliate links to affiliate networks about scammers.
Frankly, I feel sorry for Craigslist. They had such a great thing going until people ruined it.