Choose by where buyers decide, not by what is new
The right first platform is the one where your buyers already ask, compare and decide. A quick test: search the three questions your customers ask most often on each platform you are considering. Where are real people giving real answers, and getting replies? That is where attention for your topic already lives.
Learn the norms before you promote
Every platform, and every community inside it, has its own rules. Reddit is the clearest example: the company's own policies set platform-wide rules, and each community adds its own, often with strict limits on self-promotion. The same is true, less formally, of LinkedIn comment culture, Discord servers and niche forums.
Spend the first weeks answering questions, adding useful context and learning which formats the community rewards. Links to your own work come later, where they are allowed and genuinely help. Trust is the asset; follower counts are a side effect.
Measure what moves the business
Keep a short scorecard and use the same measures every week: how many people saw your posts, how many engaged in a meaningful way, how many clicked through to your site, and how many became leads or customers. Followers and likes are easy to grow and hard to spend. If a month of effort moves the last two numbers, you are on the right platform.
Own the list, rent the reach
Platform features such as native newsletters and subscriber notifications can grow an audience quickly, but the platform owns that audience, not you. Pair every platform with something you control: an email list, or at least a site people return to.
Then earn the second platform
Add a second platform when the first runs on a repeatable weekly routine and produces leads, not before. By then you know which ideas land. Cut them into the second platform's native format rather than copying the post across; the Lab's application on repurposing one piece into many shows how.