The BEST thing you can do to grow your email list is create a free offer.
The goal is to offer potential clients something of value (more than just a blog post or asking them to “Sign up for you newsletter”) in exchange for their email address. It should be something you feel you could charge for, but are giving it away as a preview to what you have to offer instead.
This allows you to WOW your potential clients and gain their trust.
It gives you the opportunity to start building a relationship, show off your amazing content, and – eventually – sell them something.