Books

Coaching Agile Teams, Lyssa Adkins
The book from 2010 is still a very good start in exploring ways to help your teams forward. It is not only aimed at teams but also at you, the coach, Scrum Master or manager.

The Five Dysfunctions of a Team, Patrick Lencioni
Although Patrick Lencioni has written over ten books in the last decades, this is his most well known from 2002. If you are enthusiastic then we definitely recommend Overcoming the Five Dysfunctions of a Team from 2005 as an follow up.