Waze takes into account your driving routines, including common locations, destinations, and times of day, to suggest future drives. When you navigate to a location it’s saved automatically in your Navigation history.
You can delete your navigation history and/or specific drives, but note that the next time you take the deleted drive it will be saved again, and may be used to suggest future drives. If you don't want to receive these suggestions, you'll need to completely disable trip suggestion notifications.