1) Identify what group of people (professional group, culture, etc) would benefit most from your product.

2) Seed early to this group and use them as a sounding board. Build a relationship with them. Focus on solving problems for this user base first.

3) Figure out a way to drive and capture the enthusiasm of this group and leverage it outside when you launch. Your PR will not just point to a product, but a social group using your product in a compelling way. Your feature list is now a benefit story.