Well I can't speak for Navy exactly, but from my Parris Island experience my advice is rather simple. Make sure you get your sleep before you leave, and once there shut your mouth, keep your eyes forward, and don't do anything unless told to. Always scream as hard as you can, put out the most you can, and prepare yourself to be thrashed for nothing, because if you don't do anything wrong, they will find something wrong. Just always remember that it's their job to be an ass, I swear they are (mostly) normal people. You're getting paid, and you're doing this for a good cause, so remember all of that and you'll be fine.