There are a lot of way people can help but the military really wishes that you wouldn't send packages as they "raise a force protection issue":
6. I see above how I can support the troops. Is there anything I should not do?
Answer: Yes there are things you should not do. There are many well meaning Web sites, TV stations, and charity groups that are promoting donations to overseas Servicemembers. While well intentioned, you should not use them and you should discourage others from using them. These unsolicited letters of support or care packages to Servicemembers raise a force protection issue, since anonymous donors are different from legitimate family members and friends. DoD has cancelled mail programs which encouraged the American public in general to mail to Any Servicemember (versus a specific deployed person). These new programs attempt to do the same thing by gathering names of Servicemembers to send mail. While legitimate mail from family members and loved ones is always encouraged, these donor programs, which collect and pass out Servicemembers’ names and addresses, is discouraged.
7. Is there anything I should know about addressing mail to a Soldier?
Answer: To ensure that mail gets through from families and loved ones, the following information is given on addressing. Recommended address:
Soldier’s Name (note 1)
Organization to which assigned (note 2)
Unit # xxxx (note 3)
APO AE 09xxx-xxxx (notes 4 and note 5)
NOTES:
1) Use of rank is optional
2) Organization name should be included if you have it; however, it is not always used for
certain types of forces
3) Unit # is a four digit number assigned to some units, but not all. Where assigned, it should always be used. Soldiers will have notified friends and family if they have one assigned.
4) APOs served by New York have a 09 prefix (09xxx); APOs served by San Francisco have a 96 prefix (96xxx), and APOs served by Miami have a 34 prefix (34xxx)
5) The last four xxxx represent a ZIP 4 add-on to the normal five digit APO Zip Code, and have been assigned to some forces. Where assigned, correspondents should have been notified and the four digit add on should always be used to help in automatic sorting of mail
http://www.army.mil/operations/iraq/faq.html