To write an ad with a high CTR, you need dividing the work into two stages:

The creative part.

Selection.

The creative part includes the collection of information about the advertised product, the analysis of it and competitors, as well as the development of at least three unique trading proposals. They should be formulated in 3-5 words so that they can be included in the headings of search ads afterward.

What do people enter into a search engine? It not just a keyword, but also a question. And the more accurately you have answered this question in your content the more it influences the clickability. It means that if you think clearly and intelligibly, or creatively "play with words" your ad will receive a higher CTR. All this leads to one significant conclusion. If you are a specialist in contextual advertising, you must know about copywriting and marketing in general.

Selection implies further split-run testing to identify more effective ones. To perform this, you should watch the rule of polarity. You need comparing categorically different headings because if you test very similar ones, you won't understand anything and don't forget to set up a uniform rotation. With the help of labels, you can test two parameters of ads in parallel. For example, we put labels on unique trading offers and the ad modifier {keyword}.

Summarizing the above

To improve your skill and reach unprecedented heights in writing ads you should read the classic literature on copyright and marketing, as the roots of text advertising go back to analog marketing, which heretofore has a fairly large knowledge base for use in online advertising.