What position is your advert appearing in? The only things that you can do to influence your clickthrough rate are to change your bid (or your quality score) to move your advert up the results, or change the text of the advert. There are many theories on how to write a compelling advert, but there is no golden template that will always work - you need to run a:b tests constantly, and learn what works and what doesn't. Clearly stating your USP's is usually a good idea, or using powerful 'call to action' words like "Buy". Free is often a good word as well. One thing that works most of the time (and improves your QS, unless you use DKI) is to have the search term in the title. What you have to watch, though, is that you don't sacrifice your conversion rate to improve your clickthrough rate. You don't pay for impressions that don't become clicks (except indirectly, through your QS), but you pay for clicks that don't convert...
Study more about copywriting and search for power words correlated with the product you are selling that can get people to click on your site.
Magazine covers are quite a good source for inspiration on how to write short lines that catch your attention - they've been doing it for far longer than the rest of us...
You might also want to check out this site discussing Call-to-Action messages. Quite helpful for someone like you ( i guess)
CustardMite is dead on. Work on improving the average position of your PPC ad and (probably more importantly) work on your ad copy. Make sure you have separated out your keywords so each one gets its own pay per click ad. This will allow you to write a unique ad for it that mentions the keyword in it once or twice. Here's a reference for you. Writing Your Pay Per Click Ads I'll second what CustardMite said. Be careful not to write your ads just to get clicks only to lose the conversion once the visitor sees your landing page and realizes your ad was not accurate. Stay true to your conversion so you don't waste money.