i've almost finished my PIP too...
the best way to set it out is in a logical order...like yeah, u have to have the intro, body, conclusion; but are u having troubles with setting out the body?
it's easy if u seperate it into chapters, like powerpuff said, but if u also put ur chapters into chronological or a sequential order...eg. if ur comparing rites of passage in Bobland and Jillland, u can do
Part 1, Bobland
Chapter 1 - Bobland, a brief overview
Chapter 2 - rights of passage until age 10
Chapter 3 - rights of passage 10 - 30
Chapter 4 - rights of passage 30 till death
Part 2 Jillland
Chapter 1 (all chapters as above)
Part 3
Comparison
Conclusion
Now that's just a rough draft and i'm not sure if you can apply it to your PIP but thats the best advice i could give!
all the best
)