Welcome to #Mastodon!
Here are a few resources to get you started.
1. A great intro: https://wordsmith.social/elilla/a-futuristic-mastodon-introduction-for-2021
2. https://fedifinder.glitch.me/ finds #Twitter people you followed, on Mastodon! You can bulk-follow them.
3. Follow many people, from many different instances, to feed both your personal as well as your instance's federated timeline. It's easy to un-follow later. Use boost often.
4. Use #hashtags! There is no algorithm selecting "top posts" for you; instead, trends are built on hashtags.