Offer good content in blog. Good content = more visitors. You can then join affiliate programs that are related to what you do. For example, have a blog that talks about Web Hosting and PCs. You can then have a small banner which has your affiliate link that will redirect them to the host you are affiliates with. For every sale, they will give you some cash or some percentage. So it goes without saying that the more visitors you have, the more that small percentage will buy something through your affiliates link.
But this requires some effort in making the content. But it will give you some reasonable though not one that will make you rich passive income.