They are referring to your Ad rank. Which also considers CTR, Ad engagement, quality, and your bid. Go and read the ad words certification training documents and watch the videos. If you take a few hours out of your day you'll know everything by the end of the month.
So improve your ads, increase quality, you have to run many ads to see which one get the best CTR.
I personally run Facebook campaigns (cheaper) to test out ads and then take them to adwords.