"It is possible for sites ranking slightly lower to get more clicks than the ones at the top," Batista says, and it starts with writing page titles and descriptions that will draw searchers in. Instead of plugging page titles with every keyword possible, think of writing them as you would the tagline for a paid search ad--brief, persuasive and focused. Use the anchor text to alert the engines to the bulk of your other keywords.
Then Batista offers two methods for calculating your organic CTRs. The first is to set up PPC campaigns using the proposed title and page descriptions in brief, and run a split A/B test. You can then expand on the copy from the best performing ads, though this will only provide an estimate of how well the copy will perform organically. Another method is to try using "Top search queries" report from Google's Webmaster Tools to compare the most searched terms vs. the most clicked terms per page.