Any advice I give may not apply to you and your business. My business is b2b and it's a platform for certain kinds of professionals as well as an API that powers many well known businesses.
I've only had success through two general strategies:
1. Networking (friend of friends, friend of customers, etc). Leverage your network to find more customers.
2. The "Long Game" (SEO, word of mouth, etc). This is where I get most of my customers.
I'd say focus on the long game from day one (blog posts, good marketing pages, etc). Use networking to determine how valuable the product is and if people give a damn about it. If no one wants to talk to you about it, no one is going to want to pay for it.