If you run a website, you need a mailing list. Read on...
EMail lists are your lifeblood. Use every opportunity you can to get email addresses. Remember these are people who are interested in what you're selling even if they're not buying at the moment. Put them on your email list and send out a special like "10% off to friends of ".
It also might not hurt to put out a newsletter related to your business. For example if you deal in pet products, maybe a weekly newsletter (sent out at the same time every week) dealing with pet health might be a good thing to do. If you need a newsletter, you can set one up through your control panel.