New member here. Been to AF twice and I've been studying the languages and culture for the better part of 6 years now. "The other side of the mountain" is chock full of vignettes of mujahedin combat tactics, both good and bad. Now, they are vignettes from the soviet war but aside from IEDs, they still fight about the same. Its a really good resource for any Joe. Its a dry read but it gives you an idea of what to expect combat-wise. Just keep in mind the IEDs lol, they add a whole 'nother dimension. That and the USMC's country studies handbook are both good. Don't get to hung up on history, though while it helps to know it, like someone else said, half of the afghans don't know their own history. They got more shit to worry about than the Durrand accord.
Other than that, I can't stress language enough. A couple fluent sounding sentences go a long way, but being able to understand somebody somewhat and give a broken but intelligible response goes a lot further. I got semi decent at pashto my last trip to Kandahar. By the end of deployment, the village elders were talking to me, a lowly early-20's SGT, instead of our late-30's PL (prior enlisted). They assumed I was the "commander" because they thought I was "educated." I owe it all to my pashto. I even had guys that I knew were Taliban smiling ear-to-ear when I spoke to them in their native tongue. There are tons of Farsi books out there, but not as many pashto. Even still, find audio CDs to go with your books so you can get the pronunciation down. If you go to DLIs website they have tons of resources, but prepare to be forced to learn the alphabet or you won't get very far. If you have any questions about learning pashto or Farsi, lmk. My pashto is really rusty but my Farsi still works.