Create your official instance

Step 1:
Use your official sub-domain to avoid fake accounts.
As an example, look at how Greenpeace did it at
mastodon.greenpeace.ch.
Step 2:
Use a dedicated server for easy maintenance.
For example, scaleway.com offers suited
Virtual Private Servers starting from 3.99 EUR/month.
Step 3:
Install mastodon following the documentation,
or the media you prefer.
Step 4:
Use a bot such as mastodon-twitter-poster
to mirror your tweets on mastodon,
or create your content directly.