You don't have to promote yourself or be fake at all. If you reply to people and they like things you say, they or others who read it may follow you. Often if you follow someone they'll follow you back--but that most likely depends on you having put some info about yourself in your profile so they can get an idea of who they would be following, and even more likely if you've interacted with them before.
Since there's no algorithm, hashtags are big on Mastodon. By subscribing to some you'll find people to follow and interact with. Also, a common way for people to find and follow you is to write an introduction post and pin it--include the 'introduction' hashtag plus hashtags of your interests. That way when people search for hashtags they're interested in, they'll find your intro post and may follow you. And whenever you post about something you want to have more reach, put a relevant hashtag or two at the end of it.