The Facebook Ad Relevance Diagnostic is an important indicator of how well your ads fit your target audience when compared to your competitors.

Having a good result here can lower your costs per click (CPC) for displaying an ad to your target audience. You'll also get the best Click Through Rate (CTR) this way. 

According to Facebook's logic, the better Ad Relevance you have, the less will be the ad delivery cost. This is because our ad delivery system is designed to show the right content to the right people, and a higher Ad relevance is seen by the system as a positive signal.

You can consider looking at your Ad Relevance Diagnostic on weekly basis & perform the optimization accordingly.

How to make sure you have got a good Ad Relevance? 

-- Target the right audience. When you run ads to target the right audience, you improve your Ad Relevance. 

-- Use attractive & catchy images in the Ad creative to improve the qu. The more people engage with your ad, the lower will be your overall ad cost. And hence, more the Ad Relevance. 

-- Keep your ad texts Simple, Genuine, Honest, & Creative. So that it is easily understandable to the people you're trying to reach. 

-- Test different creatives, ad formats, ad texts, etc & keep an eye on the Ad relevance each time and figure out what works best for your brand. Once you've had it figured out, implement the same. 

-- You can also try with Split Testing (also called A/B Testing), where you can test two versions of the same thing (this could be anything from a call-to-action button to ad copy to the image to elements in your landing page and so on) to see which version performs better.

-- Don't put anything misleading, offensive, racist, sexist, or fraudulent in your ad text or creatives. This can affect your Ad Relevance badly. If the audience hides your ad or chooses to stop being served ads from your business, you get negative feedback from Facebook and this affects your Ad Relevance.

You can understand more about Facebook Ad Relevance Diagnostic here.