Already joined Mastodon and want to bring your friends? We've got a new post you can send them that walks through all they need to know to sign up:
https://www.eff.org/deeplinks/2022/12/how-make-mastodon-account-and-join-fediverse
How to Make a Mastodon Account and Join the Fediverse

The recent chaos at Twitter is a reminder that when you rely on a social media platform, you’re putting your voice, your privacy, and your safety in the hands of the people who run that system. Many people are looking to Mastodon as a backup or replacement for Twitter, and this guide will walk you through making that switch. Note this guide is current as of December 2022, and the software and services discussed are going through rapid changes.

Electronic Frontier Foundation
@eff I would add a recommendation to try to find a regional instance, or one that is focused on a topic that is interesting to the user, large enough to be stable but not huge. For folks in the SF Bay Area try sfba.social; it is very well run and has a good community. Before joining you can in most cases visit the instance via the web and check out "Local" to see what the members are posting. I recommend against joining mastodon.social, too big, more likely to have overloaded moderators.