Keep information such as your home address out of your craigslist advertisement. Ask people to contact you via telephone or email.
If you are buying and selling stuff, use a public meeting place. Do not give them your address. Similarly, do not go to someone’s house to buy or sell something.
If the object you are buying is too large or heavy, and you absolutely need to meet in the other party’s house, take a friend with you. Do not go inside the house. Ask them to bring it out to the front door. Similarly, if you are the seller, ask a friend to be there when you make the transaction, haul the object to the front door, and ask the buyer to pick it up from your porch.
If you feel unsafe or uncomfortable for any reason, leave immediately. Remember your safety cannot be replaced by any amount of money.
If you are conducting business alone, even if you are meeting in a public place, call a trusted friend and stay on the line (using a bluetooth headset) as you complete your transaction. This is sometimes a sufficient enough deterrent to not harm you.