Community building before the launch (I will not promote)

Hey guys! I am currently working on two start ups that definitely need a community around them. One already has a product available to the public, the other one is in the development stages. how should I go about building a community around the product in both of these stages. One is in Longevity field the other is in social networking. Should I write blogs, share short form content, film vlogs and on what platform should it be created? I am definitely interested only in people who would come to this community organically. I’ve seen bunch of tool on the market that grow communities with bots-that is definitely not acceptable. If you already have created such communities, how did you go about it? Thanks in advance