For a website the only best way to earn a passive income is the placing of ad banners from different ad networks on it. With ads banners only you won't earn much money, use short link service like that ad-fly. Affiliates won't give you money if you are the site owner, it's only interesting for the site users.
That is true because a business with a smart and passive will have a result a passive income too. We need to be positive always in any kind of situation will do for us to determine that result will positive too.
In making a website too, you are going to give an extra ordinary site for your customer will have a great experience. They will look forward more and attract many visitor to look at it.