Observe how a user actually uses a product or service, when do they use? how do they use? and maybe observe any latent or unstated needs; to get instant feedback, use cameras and voice recorders.
If a set of users are available and can be filmed, capture how do they use the app? when they do? how much time they spend? is there a closure? could be a booking, a purchase, an information or just browse. Remember technology can play a significant role for better user experience.