You've heard about how important it is to stay connected with your customers. You can pay a separate service to do this (it's not free), or you could pay Passive Ninja to set up a system that is free for you to use. The biggest issue will be whether or not you use the system. Sending out emails to those who want to receive those emails is a great way to promote your service. Send them coupons or advice; it's all a reminder that you exist and that they've shown interest in you in the past.
No matter what, once they customers are targeted, make sure your site is ready to greet them. Passive Ninja designs the site that they will remember next time they need your services. If you write about it in content, it drives more people to the site. If you send that content out to current or prospective customers, they return to the site. Make sure you have something to say, and then let us help you create a system for saying it.