Obviously, making it easy to submit reviews is one key step.
The most likely reviewers are those who have purchased the product from you. These buyers might also be flagged as a "verified buyer" in your review system. I'd suggest contacting them by email
I recently bought a piece of consumer electronics gear and the vendor offered me a reward ($25 coupon or gift certificate, I think). That's expensive, but it might be a good way to start seeding new reviews.