Create setting to show ads most likely to receive conversions more often

• Optimize for clicks: Ads that are expected to provide more clicks are shown more often
• Rotate: Ads are shown more evenly

With this new feature,it will require conversion tracking.  If you have Conversion Tracking set, the Optimize for conversions option will be available in the Ad delivery: Ad rotation, frequency capping section under Advanced settings on the Settings tab of any campaign.

Below is how the setting will look like in your adwords account. Once is set, your ad is set to be optimized for more conversions.

Read the official post from Google's blog here

http://adwords.blogspot.com/2011/02/show-ads-that-are-most-likely-to.html