If you're inviting readers to download an ebook, for example, and you have a picture of the ebook included in the email, don't just hyperlink the text next to the image telling people to "download it here." Hyperlink the ebook's picture, too. People are drawn to images much more commonly than text, and you want to give your email subscribers as many options to get your ebook as you can.
As long as you are keeping track of your client’s most recent appointment times, this kind of automated reminder email is quite easy to set up. Use a custom date field to record when their last appointment time was, then set up the email to be sent 3 months later (or whatever your recurring schedule is) to remind them that they are due for their next appointment.
That isn’t to say that sales-y promotions couldn’t ever create results—as marketing “gurus” have proved. The results just aren’t as good as they could be. Take the biggest gurus’ results—the ones they boast about—and calculate their conversion rates. Often their marketing is comparatively ineffective. They just have massive volume, so the sales numbers are impressive.