Served just short of 8 years, regular Army. Scored 99 on the ASVAB without knowing what the test was other than a general aptitude service entrance exam, so I had my pick of any branch and any open MOS. Army had the choice of MOS and easier access to special schools like Airborne and Air Assault so that's what I based my decision on.
For BCT or whatever the Air Force equivalent is called, being in good physical shape helps quite a bit. Don't bother shooting for the minimum; go in with the intention to max out your PT test score by the end of the training cycle. Naturally, you train while in basic and should improve physically throughout, but the better shape you are to begin with, the better off you'll be as in it will only make training easier for you.
If you can get access to the Air Force basic training manual that you'll be issued on day 1 (US Army equivalent is TRADOC 600-4, referred to colloquially within the Army as the "smart book") it will essentially cover everything you'll be learning in basic. Naturally, all the information within remains relevant for the rest of your military career. So I highly recommend reading, learning, studying it now rather than waiting until later.
I do not recommend deliberately trying to be the "grey man" as some have suggested. If you're average, no big deal. You won't stand out and you will be evaluated as competent for service. What you don't want to do is stand out for the wrong reasons like incompetence, always being the last man, being sub par, too many No-Gos for basic task evaluations, being sloppy or "jacked up", etc.
But on the other end of the spectrum, if you're exemplary without trying to be a spotlight soldier (and I stress; do NOT deliberately try to be an alpha), it will be noticed by your trainers and you will likely be selected for a peer leadership position. Do well in that position (they cycle them until they settle on soldiers who will finish up the training cycle in those positions) and it will only benefit you in the end experience-wise, even if it does mean more responsibilities beyond just getting through training. I was tapped for my platoon guide position (the peer equivalent of platoon sergeant) during the second week of training and was left in that role through graduation. At bare minimum, it will give you a taste of what your job will be like in the future once you become a non-commissioned officer. Exemplary recruits will also be selected to participate in "soldier of the week" competitions, which again, is another way to be noticed for the right reasons early in your military career.
And yes, I realize there will be a lot of differences between Army basic and Air Force basic, but the same principles apply.
Just don't aim for the minimum passing score in anything and as obvious as this sounds, actually learn what your trainers drill into you. As ridiculous as a lot of it will seem, most of it is designed the way it is for a reason, even if it's not necessarily the best way (which is not your place to say anyway as a new recruit).
