The first step in the process is to brainstorm a list of questions that the visualizations in a presentation or dashboard should answer. If at all possible, do this with a small group of end users. If it is not possible or you are preparing a small presentation, start by putting yourself in their shoes. Try to forget what you know about the data. Think what questions you would want answered, if you were in their place. List them out.
The next step is to generalize the list of questions into the underlying concepts of what is really being asked for each one. For example, the question
Is the temperature sensor reading under 21 degrees in the summer? would be turned into
Is the temperature sensor reading significantly ...