Start to grow an email list. You can put a sign up form in your store. Then, offer exclusive sales on your website just for email subscribers.

Sign up for a Mail Chimp or Convert Kit account (they are either free or low cost email providers). Once you have some people on your email list, develop an "email drip" to automate your email marketing to them.

I also recommend investing in online advertising, especially social media advertising and content marketing, but you can start an email list for free to get it going as a first step.