Building an audience before you launch a digital product?

I'm curious as to how you go about building an audience for your digital product before you launch?

Over the last month or so I've been tweeting about new products that I've been getting ready to launch and sharing a Google Forms (http://forms.google.com/) link (some got submissions, others got none), which definitely helped with prioritizing which product should be worked on first.

Because all of my products are now being sold through Easy Digital Downloads, I decided to build a Pre-Release Notification Extension which allows you to create a product (get that indexed for SEO purposes) while sharing a link to the product straight from the get-go (https://pacificplugins.com/downloads/pre-release-notifications-for-easy-digital-downloads/)

Let me know your thoughts?