Informal rapport with the team and other groups is probably the most important ingredient in the study. Don't take your role so seriously that you forget to be human .
Sincerity is hard to fake.
You can work formally with someone or some group and yet not accomplish anything because the rapport and credibility that informal contact brings is missing. The system works through personalities. You need to talk with people on all levels face to face, not merely through formal channels. People will be more willing to listen and to send information to you because they know you on a first-name basis and feel you understand their views. Make it a point to provide opportunities for informal discussions.