The easy answer: create a community “how to get to 1,000,000 Lemmy users” and let the swarm come up with and implement ideas. In real life, this means that the mission and vision of Lemmy must be defined, based on that a positioning and messaging document must be prepared, which also describes the user profile(s). You would need to define the Unique Selling Point USP of Lemmy, and an elevator pitch. All these assets build on each other. Then you could start to create campaigns targeted at non-users, eg on other platforms, mastodon, X(!), Reddit (!), etc… draw them in with the assets and statements described above. I have done this with dozens of companies. All quite exciting, imagine a couple of tweets on X “looking for more freedom? Join Lemmy today!” Works well, takes effort, doesn’t need to cost €€€.