I recommend starting by testing headlines, as this is the first thing the user sees. Then you can experiment with text and calls to action. It is very important to conduct tests systematically to see what really works. If you read the examples in the article [email marketing conversion rate](https://www.intercoolstudio.com/ways-to-boost-email-conversion-rate/), it will be clearer to you what I mean. By the way, they offer clear advice on how to organize testing properly and what you should pay attention to first. They also advise you to carefully analyze user behavior after reading the email - this can help you identify weaknesses.