First, you check if the instance that you are subscribing to caters to your interests - signing up to a random instance is bound to be useless. Then you can jus

First, you check if the instance that you are subscribing to caters to your interests - signing up to a random instance is bound to be useless. Then you can just follow people from the local feed, or something that catches your fancy from the global feed. And if you find a mastodon user from a different instance that you are interested in (maybe in a google search), you can follow them and the system will redirect you so your instance connects you to them.