Seeing how users act in their usual environment

Try observational studies (ethnography). Observing people in real life is a great way to find out what they do and how they do it. You can: 1) Gather data on the current state of things 2) Check assumptions about how people use a product/service in real life 3) Identify existing pain points 4) Discover common user behaviors To learn more, see Nielsen Norman Group on field studies.
If you want to interact with your users, try contextual inquiry. It's a mix of observation and user interviews, so you'll gather more context around why they are doing what they're doing. You first ask users a set of questions and then observe and question them while they work in their own environments. For more, see usability.gov on contextual interviews.