User diaries is a design method used to gain insight into people's lives, particularly patterns of behavior of the potential users.
Collect a group of users and ask them to document their lives and their needs by writing a journal, recording with a video camera, or creating a photo diary. When providing prompts for the users to document, make sure the questions do not lead the user to write in a certain way. In a sense, keep your opinions out of the question to remove bias and get the truest possible data back from the users. Users should be given a time limit to this recording (1 week, 1 month etc.)
User Diaries allow the service design thinkers to gain perspective on the needs of their user to ensure that the solution they present to the community is solving a root issue, not a side-effect.