The best place to meet is your home address. This shows the buyer that you're genuine, and is as safe a place as you're likely to get.
If this is impossible for any reason, always arrange to meet in an open location - avoid remote car parks and dodgy industrial estates, and try to stick to daylight hours.
No matter where you and the buyer meet, make sure you have someone else with you. Their presence could stop anything untoward happening, and they'll back you up if anything nasty does occur.
Also, try to meet during the working day so there's time to spare in case you need to bank any money before letting the buyer have the keys.
A serious buyer will always want to have a good poke round the car, so be suspicious of anyone in a rush, or who doesn't seem too interested in looking over the car.