The ratio? 1:1(:1)
Spend as much time on subject line brainstorming as you did on writing the whole email. And then test the shit out of them to see which one performs the best (remember: you’re measuring action rate).
If you’re using a box (like this), then spend as much time writing that text as you did writing the email body. You’re looking to condense your message into 2-3 short sentences that tell the entire story, and they need to answer the top three of the four whys.
If you’re using an image in your box, spend as much time finding that image as you did writing the email body.
Then test, test, test.
You have a responsibility to your organisation and the people you’re helping send the very best email you can and raise as much as possible to help them!
Super simple stuff.