This is variously described as a weighted mark based on : Relevancy of Ad to landing page, Maximum bid, Click through rate (CTR) and landing page load speed.

 

Landing page load speed : check response times of landing pages over a few days vs. a fast site. Use a monitor to get averages, e.g. http://mon.itor.us/. Consider changing hosting provider. Improving the response time of your website should be a housekeeping job regardless of whether you use Adwords. Using a monitor will alert you to website downtime via email/SMS. Monitoring can be used to demonstrate compliance, e.g. with an SLA.

However, are the response times of your landing pages being influenced by calls to external web services?

e.g. have you integrated real-time twitter updates into your site, so there is now a dependency on a third party?

Consider storing info like this in a website database table on a daily or hourly basis, if it's not critical to website function, or implement some AJAX to handle the third party responses. This will allow the landing page to complete rendering asap. These are other ways for you to improve and control landing page response times.