From my experience, Mastodon is limited by interaction being more limited. On Twitter, I used to have the luxury of not needing to always know who I wanted to interact with. I could follow 30 celebrities I was interested in, go to their posts and find a plethora of people to interact with about something I cared about. That got me started until I found corners of Twitter that I liked.
Here on lemmy, there’s a front page that’s bound to have something worthwhile.
Both are helped by instances. If you’re in the right instance for you, you already have an okay starting point.