I'm starting off a new group right now - played a couple of introductory sessions over the past two weekends with great results. Not a one of them has military experience, although one was an Army Cadet for a few years (boy scouts who do a little drill and fire a rifle once every couple of years).
As a primer, I had them watch the first three episodes of Generation Kill and will suggest a few other movies as well (Bridge Too Far, Platoon, etc) - basically anything with a bit of realism in them and little Hollywood claptrap.
I'll also be giving them handouts using my own old notes - section/squad formations, basic ambush and contact drills, etc.
It's definitely worth running the players through a few sample combats to get them used to how nasty bullets and explosive weapons can be. Try having the players deal with a single enemy throwing hand grenades from cover (perhaps the upper stories of a building) and see what they do. Chances are they'll all suffer badly first time around, but very quickly gain a healthy respect for area effect weaponry!
Something else to spring on them in the "orientation" phase is chemical weapons. Had a single nerve gas round fall in the middle of some "veteran" players a few years back who thought they knew it all. The survivors never took their NBC suits off again!
