Achieving top-of-mind awareness is one really good way to keep your customers coming back. You could do this by sending out newsletters, which I definitely recommend. Newsletters are really good for updates and sharing product information, but they aren't terribly good at getting feedback from users. You could instead send out automated e-mails after someone purchases a product with the Follow Up Emails plugin. You'll stay top-of-mind and you can also get some feedback from the customer.