I personally have had very good luck with the book Naked Into the Wilderness. They have a charpter on tools and IIRC just on flintknapping. I finally got around to actually doing it with 'just some rocks' that I found by the RxR tracks near my station. When you read the material, you find yourself 'looking' at the stones differently....you start to look at them and think about "HOW" they would split when struck.

I was able to cleave quite a few stones and even managed to use one to cut apart a leather boot.....I was impressed and I wasn't even 'really trying' to get really good results....just playing to see what I could do.

Hope it helps.