AP courses should be very rigorous. To help students prepare for and understand the level of rigor required for this course, it is often beneficial to give them a summer reading assignment. This will also allow you to assess where the students are when they enter your class.
This handout is an example of a summer reading assignment used for 11th Grade AP English Composition and Literature.
It could be modified for other upper-level classes.
If you would like me to modify this for your own class, please let me know.