List two ways through which an author can show how a theme develops.

The most noticeable way an author develops a theme is through key words. 
For example, if I wanted to make a darker tone, I'd say "emotionless" rather than "content", or "mortified", rather than "nervous."

Also, authors tend to add small details that they want the reader to notice. Such as dramatic effects, like the reader knows something that the narrator or main character doesn't. This could also mean describing scenes or props with a greater amount of detail than expected.

I hope this helps! :)

 If we show a character who's miserable when they believe people are awful and they ... In a negative arc story, our protagonist might have a tragic ending in several ways. For our purposes here, we can simplify the theme aspect to two ... to develop a story theme of: Friends help us through tough situations.