How to get your Mastodon timeline started:
1. Follow some hashtags (more info: https://fedi.tips/how-do-i-follow-hashtags-on-mastodon-and-the-fediverse).
2. Join some groups (more info: https://fedi.tips/how-to-use-groups-on-the-fediverse).
3. Discover accounts at https://fedi.directory. If you find an account on the site that you want to follow, copy-paste its Fediverse address into the search box in Mastodon.
Lots more tips for discovering accounts at https://fedi.tips/how-do-i-find-accounts-to-follow-on-mastodon-and-the-fediverse-how-do-i-find-my-friends