Model railroads designed and built to support operations require a well thought out plan. In order to achieve realistic and achievable operations, one of the first things to consider is of course, the prototype, or a prototypical operating plan. If you can't use real life scenarios, you'll need to figure out how a schedule would fit within the space available to you, and ultimately, the time that is available to you.
This video is a high level walk through of the development of an Operations Plan, and how string charts can be used to create and modify train schedules for your layout, regardless of scale.