Firstly, do the same stuff you would do if you were selling any car. Clean it, hoover it, make it smell nice, empty all your rammel out of it and put some tyre black on.
Then stick it in Autotrader. Nobody buys the paper version, and ads go online straight away. Make sure you do not miss any calls, and can answer buyers questions without hesitation. Here's a rough list:
When was the cam-belt last done?
When does it need doing again?
Who owned it before?
Has it had a battery?
Has it been serviced? By who?
Has it broken down?
Has it been crashed?
Has it had a new flywheel (likely to be asked if it's a diesel with a few miles)?
Is it rusty, if so where, how much, and for how long? Due to a stone chip or coming from the inside? It's useful to be able to talk in terms of 5p, 2p etc. sizes if there is rust.
Last car I bought was a Golf for my girlfriend. The bloke had advertised it about half an hour before I rang him, and I bought it because he was the first person who could give me straight answers to my questions.
If it's priced well and in good nick, you will sell it quickly. There are always people looking for new second hand motors because their old one has died. There is also a fair shortage of reasonable second hand motors at the moment due to general lack of funds and scrappage hoovering up a lot of older stock.