Super interested in the replies here. We'll be launching soon and this same question has been bouncing around my head for a while.
From what I've gathered it's engaging with the community (as per PH).
@markobalazic create a buzz around the product on Linkedin, Reddit, Twitter, FB, and PH. Basically every marketing channel you have. Create a daily discussion here and don't forget to repost to other social media to get all of your subscribers involved in the discussion
Put quality of upvotes over the quantity of upvotes and thus try to connect with well established and active users of PH, if they agree to support, it will be very good for your launch