It helps if you can find a half-dozen people involved in something you like to follow at the start. Other than that, try joining a mid-sized (~1,000-3,000 users) Mastodon server based around a hobby, interest, or social group you're a part of. Most Mastodon clients allow you to keep a column open for the people you follow as well as the people on the "Local Timeline" who are a part of your server.

It's a new social network. If you see someone pop up who's made a pithy post or two, give 'em a follow. If they're not working out a week later, un-follow them. Don't feel afraid to follow a ton of people when you first get started to liven up your feed until you find a good circle of folks.