We'd really need more details. How much traffic, to what pages, from what kind of keywords, etc. What kind of conversion are you going for? A purchase, account creation, a newsletter subscription?
For some general advice, amount of traffic doesn't matter if the intent behind the search doesn't match the content on the page. If I'm searching for "founding fathers" looking for stories about parents starting companies, I'm not going to do anything when I arrive on a site about early U.S. statesmen. I'm likely to leave pretty quickly, too. Low average time on page (<30 seconds) should be your first clue that there's either:
If that's the case, focus on ranking for more unambiguous keywords, or adding words to the keyphrases you ranking for that make the context more clear. Traffic will go down temporarily, but it's only junk traffic that you're losing (which you'll lose anyways as Google learns that people search again after trying your result).
If you're confident your page content is what the search traffic is seeking, and you're certain there are no technical issues, the best approach to improve conversions is A/B testing. See: http://www.brightjourney.com/q/free-tools-help-increase-conversion-rate-site
Test making the call to action more prominent. Test having more explanation / demonstration before the call to action. Test different value propositions.
If none of that works, you may simply be trying to take them through the conversion funnel too quickly. They may be in an information-gathering phase, and all your site content is doing is selling. Try providing more resources, and focus more on getting them into a channel (email, free trial, etc.) that you can convert from once they've had a chance to learn or experiment.
Some more strategies to consider: