Google Adsense, the best money maker for most of the Bloggers and other content websites. It pays highest in the market (others may boast of paying higher than Adsense, believe me they don't). If you don't already have it then get it the first and foremost thing.
And if you already have it but still not getting satifactory earnings, try placing ads in different places.
For me the one with main content works best. Other options that worked well for me - top of the sidebar (left better than right), and one below content. If even after placing your ads at good site you are not getting good revenue, then maybe your genre is quite low-paying for which only solution is change the genre(which is very very risky, as there's lot of competition for high paying genre's). Other tips with adsense -
- Text ads pays better than image ads.
- Design main content ads to integrate them with your template. You can have sidebar ads in contrast color to highlight them.
- Link units are not that good, but still they can add some little revenue, consuming very little space.
- Try showing your main content ads only on the post page, rather than on all pages(including homepage, you can show sidebar ads though.)
- Try to limit your ad units to only two per page and link units should be one per page.
- Get some SEO done, search traffic can get you really good money.
- Have some patience, earning money from Blogging is not 'Rich in a day' type of thing, it takes time.
Happy Blogging to all :)