You gotta follow some people, and also hashtags. Following hashtags made a huge difference populating my feed. There's no algorithm so you get to/have to choose what you want to see.
I also use the ice cubes app for mastodon, which has a trending option also for when I want to see what's gaining traction outside of my follows.
Also don't be afraid to use filters to block keywords if you need a break from certain topics. It's amazing how calm and actually interesting the feed is if you block all mentions of Twitter and Threads and US politics
Wow, you and the commenter above really sold me on it. That's the way the internet was meant to be used. You go and search for shit. Not shit getting fed to you because "it totally matches up with other things you like". I've hated these algorithms for so long. And for me personally completely misses the mark on what actually excites me. Instead it intentionally shows me bullshit that I will scroll through for hours or plaster my face in front of the second I have exactly 30 seconds of free time in my day. It's fucking junk food.
Follow your friends, check out your instance's federated feed and follow some people there (if you aren't self hosting), follow some tags, and follow a trending bot like @popularposts@masto.ai