Do you know that there are people called website brokers, who can help you sell your website fro a certain commission. They know many poeple and companies and often it is easier to use them rather than trying to do it your self. Unfortunately I cannot recommend anyone.
Also using sites like sitepoint and flippa will not hurt, however, please do keep in mind that flippa has a term, where you are not allowed to publish the website for sale on any other place, while on flippa.
Oh, almost forget, I have seen sites for sale on eBay. In any case, make sure to provide the essential figures such as visitors, page view, average time on site, bounce rate, seo details etc.