More and more people outside the US want to invest in US financial markets.
A book, written specifically for non-US citizens living outside the US, covering all aspects of investing in the US financial markets. Chapters on existing financial markets, investment vehicles, how to open the needed accounts in the US, taxes, etc.
If what you are selling has a long run effect on your customer (exercising, financial security, passive income, etc.), it can help if you connect them to their future selves.
In your communication, show them or send them their picture (you can ask it from them for a surprise you’ll be sending them) age processed, software can create their image an X number of years from now. Of course, your message should be congruent with this idea, and help them realize that their future self is the same person they are now, and why it is important that they invest in their future (by paying you.)