Here are some tactics that can help you build your social media presence before a product launch:

Conduct thorough research on your audience
Release teasers before launch
Create branded hashtags
Convey a story through your posts
Collaborate with local businesses or artists
Host giveaways
Start your own blog and publish content
Use long and short forms of video content
Make reminder posts on Instagram
Create a live-stream event with founders
Storytelling posts from founders