If your business has long-standing customers, you should keep a mailing list and keep them informed of your activities and services. If you need to recruit new customers, tempt them to sign up for your mailing list. By building an opt-in community you know who your core customers are and can reach them easily.

Think of a seasonal illustrated newsletter with articles of interest. Or a quick mass-mailing to your registered users about your forthcoming event. Or informative PDFs to help market your wares.