If you can possibly help it, don't sell your car after Christmas, when no one has any money. Consider holiday periods: will the people be in town or away. Sometimes this can work in your favor because if people are not at work they have more time to look for cars, and they are usually cashed up with nothing to do.
On the reverse side, when buyers are busy working, they don't have the time to do a lot of car shopping, which can make negotiating easier.
Additionally for this reason, if you get a buyer to come on a week-night, it is unlikely he can compare yours to other cars – which can sometimes work in your favor.
Tip 2 – First Impressions are everything Just like you are going on a date – first impressions are everything. Get all the rubbish and junk out of it. Deodorize it. Wash it, clean it.
Tip 3 – As the good boy scout says. Be prepared. Get your paperwork in order. Find the spare keys. You don't want to be rushing around at the last minute, just when the buyer is ready to go for it. You can't find something. He may just say, he'll get back to you. Believe me, it happens. So get organized before hand and you'll have a much smoother run of it.
See my other articles for more tips.