Diary studies will give you insights over time,on real-time, in their actual environment and without being biased by the presence of a researcher observing. It consists on recruiting users, explaining them the process, what you expect from them and giving them a diary (paper, mobile tool..) where they can tell about their experience.
The user can be asked to report his experience at fixed times, when an alarm asks him or whenever a particular interaction/event happens during his day. You can give him total freedom on how to report (text, photo, video, voice...) or provide a template for him to fulfill. It can last from a few days to a few months.
With this method, you can focus on habits, usage scenarios, the movitations pushing, the feelings, the thoughts behind an action and it will definitely help you visualize the customer journey (in service design).
Users need to be really involved, dedicated, and sometimes writting a diary can take a lot of their time. You need to make them feel how important it is and give them a reward, an incentive (the reward can be splited in 2, a first part during the process and a second at the end!).