I've been asked many, many times how to write historical fiction. In addition to the classes I've taught on the subject at the LDStorymakers' Writers Conference, I've spoken at length to individuals on the topic. What it all boils down to is this: get your facts straight and make them interesting.
I can't even tell you how many times I've had a friend read a manuscript for me to be told that I got everything wrong. I rely on friends to keep me on the straight and narrow, to help me see where I've gone off track -- or not given proper attention to the political ramifications of the event -- or given the wrong impression. Without this important feedback, I would not be a published author. Your facts have got to be straight or you will come off looking like an idiot. I've been there, done that, and it doesn't feel very good. After all the research you can do, always have someone with more knowledge than yourself read it for you. Research can't take the place of the personal knowledge that comes from having lived through the experience yourself. This is why I like having really old friends.
Now, you must make your facts interesting. This can sometimes be the hardest part. You've gotten your information from a very dry textbook and you must now translate it into something that the reader will devour. The most effective tool you can use is emotion. Your character has just witnessed the death of Abraham Lincoln. How did she feel when she saw him fall? Did she see the gunman make his escape? How did she feel when he was captured? A recitation of facts is all very well and good in a college classroom setting, but your reader wants to be enthralled. Use your imagination and put yourself in your character's place. If you were there, what you would have felt?
And as always, watch for repetitive word use, punctuation, and grammar. Nothing breaks up the emotion of a scene like a mistake. It will leap out and wave a flag in the reader's face, pulling them out of the moment and reminding them that it's just a book. But we don't want them to remember it's just a book -- we want them to get sucked in completely. Choose your words carefully. Edit like crazy. Study your manuscript for anything that would jar the reader, and when your work is ready to be published, study the galleys very carefully. Don't shatter the illusion with a badly spelled word or a misplaced comma.
Stay tuned for more, and in the meantime, visit http://www.internetwritingjournal.com/apr06/crook.htm This is a fabulous article on writing historical fiction.