Create a nice atmosphere.
Make it simple and remove any technical barriers. They should be able to google "Fediverse" click on the first link. Choose a username and be on their way. Find the app with the same name and install it in 2 minutes.
The network effect is a thing. They need to already find lots of their friends, interesting people and their favorite stars there.
And it has to be easy to discover them, if we don't have an "algorithm" that suggests content.