Read the full article here @ Google > Support: Create a responsive search ad

In this article, you’ll learn best practices for writing responsive search ads and some common mistakes to avoid. Remember to create only one responsive search ad for each ad group and make sure there is also at least one expanded text ad in the ad group.

Tips

Providing redundant headlines and descriptions restricts the system’s ability to assemble ad combinations. To increase the likelihood that your ad shows, focus on these key best practices for each responsive search ad:

  1. Provide at least 5 distinct headlines that don’t repeat the same or similar phrases.
    1. Providing at least 8-10 headlines is best. The more headlines you provide, the more options there are to assemble your messages into relevant ads, which may increase performance.
    2. Be sure to include a keyword in 2 headlines.
  2. Be sure to have at least another 3 headlines that do NOT include your keywords.
    1. Try highlighting additional product or service benefits and features, a problem you’re solving, or highlight shipping and return information.
  3. Try creating headlines of different lengths. Don’t  try to maximize the character count in every headline.
  4. Add at least 2 distinct descriptions.
    1. Remember: responsive search ads could show up to two descriptions at a time.
Note: Ad customizers are currently not supported by responsive search ads.