If you're thinking of reading A Brief History of Time
, read this first. At least if you're a total civilian, which I am.
My son and I read this together. We did have to hit the Internet pretty hard a few times to get clarification on some critical points; but all in all, this is a well-written, accessible introduction to some pretty heady stuff.
I would recommend having the basics of atomic structure and the life cycles of stars under your belt before giving this a go. Also, it really helped my son and me to resign ourselves to not being able to visualize certain concepts. Wave-particle duality is just plain weird, and I think it helps to do the best you can and ultimately just go with it, rather than struggling to fit this contradictory idea into a conventional kind of "making sense."
And now: on to The Illustrated A Brief History of Time
(expanded and updated edition)!