Teaching scales in graphs
A classroom discussion on the context of the data reported in media articles is a good beginning. Students could then explore why the topic might need to be reported.
Using a well-constructed graph as an example, discuss the key aspects of a correct graph, including the appropriateness of titles and labels. Emphasise that the selection of scale is vital.
Now, students can be sleuths!
There are many examples of misleading graphs in textbooks. You can find some examples and some questions in Misleading Graphs and Statistics (228 KB PDF on Arkansas State University website).
You may be able to find examples of misleading graphs from the media that would appeal to your class.