If you are working on a US military base then don't sweat it, it is very very safe! Kabul isn't too bad but other than that it is kind of dicey. My favorite city is Herat. Also remember that no matter where you go things may be drastically different from where you were. There are many ethnic groups with different cultures and or languages. I highly suggest reading as much as you can! A few good books are Tournament of Shadows, The Great Gamble, and my personal favorite Words in the Dust by Trent Reedy.Â
The reason I recommend "Words in the Dust" is that it is a great story that is easy to read AND if gives you an insight into what the culture is like and how Afghans interact with friends and family and toward foreigners. Again, this book is a great resource and a good place to start learning. There is also that you can view on YouTube.
Good luck with your life journey, where ever it may lead.