On Mastodon, I used the search function to shotgun random topics that interest me, and then followed all the hashtags on the posts that came up.
Over time, I started replacing following hashtags with following my favorite users who I discovered through those hashtags.
Then I started discovering and following their favorite users through their boosts.
Now that my feed is pretty much where I want it I tend to click “hide boosts” on anyone new that I follow, to prevent their every random amusement from cluttering my feed.
The end result is fantastic, but it took awhile to get there.