congrats to you my man! Let me just say this, basic is all mental, it is just that they go through the body to get there. Get in the best shape you can before you get there. if you can do 40 plus pushups without stopping, and run 2 miles in 15 mins or less, this will be good. just remember , they are still going to dog you out big time, no matter what shape you are in.
It took me a while to fully understand this , but the saying , "they can kill you but they can't eat you", finally made sense to me. I could try to explain this , but for me it was a matter of getting it, detach my feelings, they are not out to "get" me , it is nothing personal. Soon afterwards, no matter how tired or ached i was, inside i was almost laughing. they do this to everybody, to weed out the mentally weaker. You have to let it go. For other guys , this saying may have a diff meaning to them personally , this is how the light came on in my head, and basic , ait, etc., just didn't bother me anymore.
one more thing, the first 6 or so months you will probably hate everything, and want to get out bad. after a year you may say hey, i could do this for a while. So anytime any advanced schooling or training comes up. or OCS, or any cross training , or naval academy, or anything at all to advance yourself or become an officer candidate, JUMP ALL OVER IT!