Here's what I did with Google ...
When I took over our Google stuff our conversion rate was quite poor, although our CTRs were high. I did a few basic things to change that:
1) I did an experiment to determine what messages customers responded to the best. To do this, I inserted about 20 different ad copy variations for each adgroup and let Adwords self-optimize on CTR for about 2 weeks. Adwords will eventually pick the winning ad by giving it proportionately more impressions. (This is a feature that Yahoo doesn't provide, which frustrates me. On the other hand, you get a lot more characters in a Yahoo ad, so you can cover more bases.) After a couple weeks, I started deleting the lowest performing ads until I was left with the 1 to 3 best. (Recognize that inserting all these ads, which will include low-performing ones, will knock down your overall CTR during the optimization period.)
2) I made sure that the essence of the search terms was repeated in the ad copy, ideally in the ad title. (This improves CTR, but not conversions.)
3) I made sure that the landing page repeated, clearly and often, both the keyword string and the message that had resonated with customers (see item 1). This consistency of message seemed to be the key to driving up conversions. Since we have 3 or 4 active adgroups with different keyword themes, and each of those adgroups has 1 or 2 messages that seem to resonate, that meant that we now have 6 or 8 unique landing pages. They're all basically copies of each other, with keyword and message phrases sprinkled in strategic places. (They are not linked to from within the broader site, but merely serve as an entry point into the site.)
After about 2 months, the search (not content) CTR has leveled off at about 8% and the conversion rate at around 25%.
One very valuable side benefit has been that adding those multiple landing pages with a high density of keyword strings has meant that our organic search results have improved significantly, as well. In our top performing adgroup, we also are consistently in the top 3 organic search results. I read somewhere that searchers click through the organic results 70% of the time, compared to 30% for sponsored results.
Hope this helps,