Segment and structure your ad groups
The biggest dictator of the amount you pay for each keyword is the quality score. You quality score is based on the keyword you use, and the landing page it is pointed at. If you segment your ad groups down to the keyword group, you can display ads that closely related to those keywords. This will improve your quality score. As Google pointed out, if you increase your score from 3 to 6, you will half the amount you have to pay to target that keyword.
Focus on interesting and informative ad creative
Two things to keep in mind when working with Adwords, you can reduce the amount you pay per click, by increasing the quality score. According to Google, the most important factor in calculating quality score is your click through rate.
Interesting point to note
Adwords tracks your URL from account to account. So if you think of closing a poorly performing account, and using another one with the same target URLs, then Adwords remembers and moves all of your history across, poorly performing quality score and everything.