Flatter your audience
Show your audience that you're interested in them. It's funny to me how we've established best practices in places like Facebook that tell brands to ask questions to build engagement, but rarely does the brand show it's listening to the response.
Your success in Pinterest also relies on your ability to show you're interested in what others are doing -- not just in what you're posting. And hey, doesn't flattery get you everywhere?
In all seriousness, at the simplest level, re-pin content from people who are following you and tell them why you're re-pinning it. Does it give you an idea? Did you think it was a cool use for something? Does it maybe even inspire you about a new product idea?
You can take that further too. Ask people to build your boards with you. Ask them to pin pictures of themselves using your brand and re-pin those on a special board that acknowledges them. Whether you run it as a contest or just publicize the fact that you want to hear from them, let people know you're listening and that you value them as people and content contributors.