It seems to me that the question is wrong or maybe in the wrong order. First, even before building the product, you should have been talking to customers and finding out what they need and want. Customers don't always know exactly, but they can give you a ballpark idea and tell you their desires and strong dislikes.
Once you have that (plus names of potential customers) then you build, tweak, build, tweak. (Getting customer input along the way)
While you're doing that, you're building your brand, interacting with consumers frequently. This is the process of paving the way, beginning to get brand recognition, finding out the best ways to reach potential customers.
Then you get to the point where you have a good enough product you can release. You plan the release around a marketing campaign that begins several weeks before release. You build up anticipation, keep building brand and anticipation.
When the big day comes you shout out to every customer involved all along the way. You ask them to become brand ambassadors and tell their friends.
You put your heart and soul into branding, branding, branding, in a way that helps your customers. Your product meets some deep need you uncovered earlier. They can't live without it. (If not you made a mistake earlier.) You work day and night getting your product into influencer's hands and in front of customers and keep going until the traction starts tipping your way. You expect it will be really really hard to be recognized and heard in the vast noise of our overinformed world and keep plugging away.
I wish there was a magic bullet. Maybe there is if you're the lucky superconnected person in Silicon Valley. For the rest of us, not so much.