EV from Somewhat in the Air has a great post on antithesis.
An antithesis … can be built by contrasting any of the different parts of a statement. But there is always a balance in the actual physical construction.
— EV (2011) in Antithesis – 15 minutes of writing
For example:
“Extremism in the defense of liberty is not vice, moderation in the pursuit of justice is no virtue.” –Barry Goldwater (1964)
It makes for a nice little (15 minutes perhaps?) self-contained exercise.