Go to http://www.easports.com/gameface
and follow instructions there. You'll need to download UnityWebPlayer. (Thanks KaNtST0PmEh)
After you do that, if you don't care what it looks like (Such as myself) just select one of the pre-made faces. Save it, then enter Madden 13 and select connected careers. You should see an option to use Game Face. Download this, and after a while the achievement pops.
Be warned though, at least for me the Game Face process was very slow, so don't get too frustrated.
I'm also being told that this isn't working for them, so it could possibly be buggy :/
Nyte Rayne 2 said, "It loaded very fast for me...achievement did not pop until after I chose my position, team and draft order. Just a FYI that it pops late"