Advertisements are the main source of income of a website. According to the way of traffic and the interest of advertisers advertisements are of different type like CPM, CPC, CPV, CPI, PTP etc. If a site have huge traffic which means traffic higher that 2000 unique visitors then it is better to use CPM ad network because it can generate more income with the impressions that get from page views. But it is not possible if the traffic is below 1000 unque visitors so for that it is better to try CPC ad network because it will help the webmasters to get paid to every click that they recieve. My recommendation is use CPC ad network if the site traffic is between 100 to 800 page views. But if the traffic is less than 100 page views that is mostly a beginning site need CPV or CPI ad network because it is not possible to generate income with impression and it is very hard to ad clicks to a less traffic site so using CPV ad network will help the blogger to get paid per impression or view and CPI ad network will help the blogger to generate income by get paid to send an installer for a software.
CPI ad network is a very good media for a less traffic sites so for that the blogger need to post articles related to a particular software and provide the referral link to download. For low traffic generating sites PTP ad networks are also good. One thing the blogger need to understand is don't use traffic exchanging tricks to generate income because it may cause even banning from the ad networks. So for generating income from a website one should have to follow the way of ad network which is best for their website traffic. All the best.