Provide ample free space around your ads

Do not make your ads look cluttered. Have enough free space around them to make them look
neat.
And if you have blended it well, your CTR would see an instant jump.

Image ads increase variety and competition

By choosing to display image ads in addition to text ads, you can help ensure that you'll have all available advertisers bidding to appear on your site. Both text and image ads will compete in the same auction to display on your pages, and we'll automatically display the ad(s) that will be most effective for you on your site.
Interested in giving image ads a try? Make sure when you're creating a new ad unit, your ad type preference is set to text and image ads. Then, test the image ad option on a small subset of your pages for at least 2 weeks and track the progress using channels. This will allow you see whether image ads are effective for you.