Tips and Tricks HQ  (a blog that publishes articles for e-commerce site owners, WordPress administrators, and web developers) wrote this helpful article about generating leads for your e-commerce business.

A few simple suggestions:

Word of mouth
Ask for referrals. Incentivize your current customers to do this with discounts, coupons, giveaways

Up sell and cross sell existing customers
Suggest complementary products for an existing order. Offer bundled discounts.

Offer Free Products
Add a small item to a new order for free.

BLOG!
And invite a guest blogger who can write about your market/industry in general.

Network
Reach out to your existing business relationships.

You can read the entire article here.