Depending on the value of your vehicle, it’s sometimes a good idea to invest ~$100 prior to listing to streamline and expedite the process. $10 on a Carfax vehicle history report and ~$75 on a pre-purchase inspection at a neutral car shop. Preferably the dealer. Showing a potential buyer these two things helps greatly to show that you’re an honest, motivated seller.
Be clear in the ad. List everything you know to be wrong with the car.
Decide on a price and list it as “FIRM” multiple times in the ad. You’ll encounter people offering half your asking price and a riding lawn mower unless you make it clear from the outset. Especially on craigslist.
At the very least, top off the engine oil, have the proper air pressure in the tires and do a thorough wash and detail.
Definitely ride along on the test drive. Not only do you want to make sure they don’t steal the car, you want to make sure they’re not dogging on it as well. Don’t be surprised if they want to take it by a shop to have a pre-purchase inspection if you don’t do it beforehand. Choose a shop together to make sure the mechanic is not their friend.
Also remember (a lot of people succomb to this…), when people start haggling with you because there’s a dent here, or this belt may need to be replaced in six months- you’re selling the car cheaper than it was new precisely because it’s used. They’re not expecting to see a new car and you’re not advertising it as such.