NAMI is hell for most NAVY/MC guys. A lot of guys in training with me got the NAMI Whammy and are now in NFO slots. MEPS may clear you, but they are just looking to make sure you do not have cancer or are deformed.
I am in Strike NAV training at NAS Pensacola. USAF 2LT. I will track into fighters going for a f15E slot hopefully. I am a WSO or backseater. I am in Instrument Ground School and will go back to the plane in a few weeks.
Flight School? Be ready to study, memorize, fly the mission repeatedly in a chair facing the wall, while doing all the hand motions, callouts, and radio calls. Be ready to memorize a HUGE amount of info. Then be ready to study some more. Did I mention you need to study some more? Be able to trace all the systems of the plane in explicit detail from memory. You will memorize about 6 pages of BOLDFACE. Look up T-34 or T-6 Boldface on google when you get the chance. It is called Immediate Action Items in NAVY Terms. Then Study some more. They will hand you a stack of books when you check into training. If you are smart, you will read all of them and make notes before class starts. Then read them again during class. Be ready to have a reason for anything you do in the airplane, they may not ask why you decided to turn left when you did, but you had better be ready to tell them if they ask. Essentially, if you can tell the instructor the procedures for what he is about to teach you, you will be fine.
If I had studied as much in college as I did in the first 2 weeks of flight training, I would have graduated a year early with a 4.0 GPA and honors. Good Luck, sincerely, from a guy already in the middle of it. But I do know what kinds of things recruiters say, and have seen the poster that says the marines will give you a flight spot for signing up. Just remember that to be a Fighter Pilot you need to be the HARDEST working dude in a school FULL of hard working dudes.