Advertising is by far the most popular monetization methods for blogs and websites. That is because running some ads on a site is both easy and efficient. It’s easy because you just need to copy and paste some code and you are set. It’s efficient because if you stick to the major advertising networks your earnings will be pretty decent.
Despite these advantages, I often hear bloggers and webmasters complaining that they are not making as much money as they would like with the ads on their sites. Sometimes this is a problem with the site itself. For instance, if the the number of monthly visiors is too low there is nothing one could do to boost the earnings. Many times, however, the site gets a decent amount of traffic, so the earnings are low because the advertising setup is not optimized….
Source: Visit Daily Blog Tips
If you make money online using your blog by displaying Advertising like AdSense etc. You need to read this post.