The big question is: What are you interested in and on what instance are you? For new users the local timeline is the best way to start building your network. Of course that only works if you picked an instance that caters to your interests.

Honestly that’s my biggest problem with the official app always pointing you mastodon.social. It hides away one of the best on-boarding features in order to be more familiar rather than trying to make it work.

Another way to find people is the fedifinder, a tool that shows you who of the people you follow on twitter also has a mastodon account (assuming you are on twitter)