Cost per Click is the amount an advertiser is willing to pay for the clicks that are generated on the ads shown on your page. AdSense has a bidding process in which different advertisers bid for the ad space on your blog and the highest bidder gets a chance to display their ad. AdSense on its own ensures that the most paying ad is shown on your page so that you earn maximum. Its not in your control to decide to decide the ads or to fix the amount for charging. However, by following some of the basic practices, you can increase you Cost Per Click for the ads and earn maximum from the adsense. 
Practices to increase AdSense Cost Per Click.
  • Enable all of your ad units to show both text and images rich ads. When you limit a unit to show only a particular kind of ad, either text or image ads, you are limiting the number of bidders and thus lowering your chances of earning maximum. Lets get it with an example. Suppose you have limited a ad unit to show only text ads. And you receive a CPC of 1$ on it. What you miss out is that there may be an Image ad that is willing to pay more than 1$ per click. By increasing the number of advertisers to compete for the ad unit, you are increasing your chances of getting higher bid than you get normally. So, its always better to enable all ad units to show both images/media ads and text ads.
  • The first ad unit that appears in your blog's html receives the ads with maximum CPC. Suppose you have put three ads units, one as a leader board, a sidebar, and one at the bottom of your posts. Now, naturally you will wish that the highest paying ads are shown on leader board, since there are more chances of people clicking on them, so you have to put the leader board AdSense ads first in your html code. You may achieve this by trying and testing. 
  • Keep your filter list small. Filtering majority of ads for whatever reason will ultimately lead to less advertisers competing for your blog, and hence less earning.
  • Developed countries CPC are usually higher than under-developing countries. You will get a higher CPC from US than from India. So, building a country specific audience will limit your reach. Its also not at all advisable to target only US audience. You are paid for Indian clicks too. Whatever it is. The point is, don't limit your audience to a particular country and try to build a follower list of countries like US, UK, etc. 
The ultimate goal is to allow maximum number of advertisers bid for the ad space on your blog. The more competition, the more earning. By enabling both rich media ads and text ads does this only. 
However, in doing all these practices you must avoid some points. 

  • Don't believe that writing for high paying keywords will earn you more CPC. This is a good practice unless you over do it. You are writing for people who reads you. Don't over do it. Moreover, Google says that it don't encourage any such practice.
  • Don't use multiple accounts. Its a violation of terms for Google and your account will be suspended as soon as they discover it. 
  • Don't change the behavior of AdSense Ads in any way. Its not permitted under Google terms and conditions. 
Most of the publishers learns from experience. Keeping these points will certainly help you in increasing CPC for AdSense ads.