This guide is a list of suggestions you can implement as a Scrum Master when you are joining a newly formed scrum team. However, many of the suggestions described here may be useful in case you become Scrum Master for an existing scrum team.
Read the complete article here: https://medium.com/@clausreestrup/the-scrum-masters-field-guide-to-a-newly-formed-scrum-team-first-steps-462f41026884