I've looked about on here and it looks like I'll need a bigger sized envelope for the book for the customs form. I'm wondering what information I'll have to include on the form. This website I went to listed this information:

1. Sender's name and full address
2. Addressee's name and full address
3. A detailed list of the contents including the:
   • Quanity
   • Value for each item
   • Net weight of each item, if known
4. The type of contents
5. Disposition of mail in case it is undeliverable
6. Sender's signature and current date

Is there anything else not listed? Thanks in advance!

If it's under 16 ozs (one lb) you should be able to use the small green customs form.  there is nothing in addition to your list needed.

IIRC there's two forms.  For a book you will need the smaller/shorter form, it's not very long so you can ask at your PO (if they are nearby).

Some small packages seem to travel APO without any documentation, as the guidelines don't appear to be well understood by USPS employees.

We've several helpful PBSmember/USPSemployees, someone will be around shortly with better advice 

If they ask for a phone number just put yours down.  Or at least that's what I do.

As everyone probably knows, the requestor conditions says to use the white form so I think I'll stick to that if I can to avoid any problem. It's actually going to a DPO address, but I don't believe that makes any difference. Thanks again everyone!

The small green forms aren't green anymore. They're white carbon paper now, but still about the same size.

There could be some old ones floating around, but I guess I was using the old ones for a while after the new ones came out (because my postmaster never told me about the new ones), and my postmaster got a big lecture. 

Sticking to the white form is a good idea. Some of the military members have said that the small green forms are not allowed for military, it gets past the USPS requirements, but the military itself requires the large white one. Packages usually get there with the small green one, but sometimes slows them down quite a bit because they don't have the proper documentation on them.

The USPS people at the counter have always been very helpful when I mail to an APO so don't worry, its a pretty simple process.

Thanks for the added info, Becca and Melanie. I believe I will indeed stick to the bigger white form. I'd hate for any book to get slowed down unnecessarily, but more so going to a military member. I'm heading down there today feeling better about the process.