Soldier's Creed, Warrior Ethos, The upper chain of command(Obama down to the Sgt. Major of the Army), Basic knowledge of Marching and Movements. This will all go very far if you know these things before you go.
But your recruiter will have classes on all these subjects plus more. You'll get Map Reading Courses, and LDRSHIP Course. Loyalty, Duty, Respect, Self-less Service, Honor, Integrity, Personal Courage. LDRSHIP. Learn that as well. Study for that ASVAB bro thats the beginning. Go to the library or search the internet. For a study guide of the ASVAB.
Score high, the higher the score the more jobs open up for you. Try to get your credit straight, pay your bills. If you have Chitty credit you won't get a Security Clearance which cuts out certain jobs. Again ask questions to recruiter, he/she will guide your way.