What do you know about your landing page? Have you tested it? Does it have trigger elements that are sending people off your website in an instant.. or possibly trigger elements that are making people buy?
In the day of the week example mentioned previously, the client’s Thursday to Saturday problem was rectified by simply adding ‘Ships within 24hrs’ (which they did). In another example, a client with a prominent dating site focused around matching professional singles, found that whenever their landing page features picture of people under 30 conversion rates would plummet. Why? The landing page didn’t ‘relate’ with the users coming to the site (slightly older). Removing images of people and keeping the site ‘neutral’ was the key to turning this campaign around and driving website sign-ups.
What you can do to fix it:
Try using heat mapping tools like crazyegg.com to understand the habits of visitors to your landing pages. Also ensure you have linked your Adwords with Analytics to better understand user behaviour from specific keyword which provides great insight.