Number of Clicks / Number of Impressions
The CTR is the metric that will tell you how often your (seen) ads are clicked on, ie. how attractive your product is at first glance.
A solid CTR is the basis of actually being able to convince customers of buying a product on the listing page.
The most Important Factors for a High CTR
The main product picture is usually seen as the most influential factor. The picture should lead the product to "stand out in the crowd" of competitor products in the search results of a main keyword. This can, for example, be accomplished with differing colors, contrasts, point of views, special effects or other oddities.
The title should make the product's strongest arguments clearly visible. Please note that on mobile devices only around 70 title characters are visible, so these arguments should be placed at the front.
In general Prime Products will have a higher CTR and Conversion Rate.
In most cases lower prices tend to have higher Click-Through-Rates, but the most important factor is that the price is not significantly higher than competitors' prices.
In some luxurious product categories, a higher price may actually lead to a higher CTR and Conversion Rate, as customers will usually equate higher prices with higher quality.
Average Rating / Reviews
This figure will of course also have a big influence, if it differs strongly from the rest of competing products.
Investing resources into becoming a strong brand will pay off in the long run - especially regarding the CTR.
Please note: The CTR can only be retrieved for Ads (PPC), as Amazon is so far not making impressions of organic search results public.