Tom Cal, CFA ⋅ San Francisco, CA Army Veteran, Investment Manager ⋅ 25 years experience

Practice, practice, practice.

Is the GT score broken down into more detailed components? Are there any particular areas where you want to improve? (Math, verbal, etc.)

For verbal, subscribe to the New York Times or other journal you find interesting ("Agronomy Journal", perhaps?), and spend an hour or more reading it each day.)

e.g.
https://www.agronomy.org/publications/aj

Is any of the information below helpful?
http://www.usarec.army.mil/hq/warrant/WOgeninfo_GT.shtml

http://helicopterforum.verticalreference.com/topic/16456-gt-score-improvement/

https://www.google.com/search?q=improve+GT+score&oq=improve+GT+score

Robert Da Costa ⋅ Orlando, FL U.S. Army Reserve, Chief Warrant Officer ⋅ 17 years served

Luke,
As a warrant officer myself and former battalion training NCO, ASVAB for dummies, or any other similar self-help guide, is your BEST option. All of my personnel who previously desired and were required to increase in their ASVAB scores whether for direct commission packets or MOS changes scored in the 120s and above range after spending an hour every evening for a minimum of 2 weeks prior to retaking the ASVAB test.
If time is not of the essence, then enrollment into some college level classes may refresh your memory especially with regards to math questions which tended to be the predominant problem with my test takers.
I hope this helps.