Tonight the instance picker on instance.mastodon.xyz will go live, @thekinrar is currently working on the last updates.
If you want your server to be on this list, you need to sign up and answer a few questions. This is to help users find an instance, which offers things which is important to them.
You may already have signed up your instance to the admin space, but not added any info. Now is prime time to do so, so users can find a home with you!
Go to this link, and follow the instructions.