What is your education level? If you're college educated, apply as an officer only, never as an NCO. If you're not, then use the military to pay for your education, then look to get your officer's commission.
Also, pick an occupation whose skills are civilian sector transferable, like mechanic or computer technician. Try to perform your physical and combat test with just the bare minimum. Leave the high marksmanship and assault course scores for the front line combat specialists and athletes who will most likely get blown up by some random IED in the Middle East or Africa.
Your goal should be to stay away from operational theatres as much as possible. The order of military branch preference should be navy>air force>army.