Hmm. I guess there's little chance that people who think they can write historical fiction without cracking a book are reading this, so congratulate yourself for not being one of them.
You must know your historical period. Period. Carolyn's Workshop goes into further detail if for some reason you don't intuitively understand why this is so.
Here's a list of some useful books.
Also, from time to time and in response to questions, I've compiled information on various topics. Since I hate for the work to go to waste, I've posted some of them here.