I’ve always thought that if I were a history teacher, I’d ask any reluctant students to write a story set in the time period they found uninteresting. As soon as you begin to create characters, you find yourself in the midst of learning about how they lived and what was important to them. That makes learning the details fun and painless.
My favorite way to research is to read as much that was written in the time period as I can find. Diaries, letters and novels contain personal incidents and small details that can help set the stage for the reader. Often a simple detail, such as black marks from smoke on the ceiling, can create a whole scene for a reader. Discovering what was different then from the way it is now can be very illuminating both for the writer and for readers.
As much as possible, the research and detail should be revealed as part of the story and the characterization. Characters interact with their environment—they use items, they use transportation—the writer has to introduce these things without causing the reader to be distracted by them. I tend to trust the reader to create their own images from a significant detail.
Often research can even suggest romantic conflicts. In Lessons in French, I used the fact that the crime of forgery was punishable by death in the 1820’s. This created a real danger for the hero, and a reason why he couldn’t freely offer marriage to the well-bred heroine. Magazines for ladies that covered both fashion and gossip, much like today, were passed around villages in a set order of precedence—important people got them first, unimportant people got them last. The hero’s mother has a stack of very outdated magazines to read—a small detail that helps create characterization and indicate her lowly position in the social order.
In the case of complicated legal issues that impact the character’s lives, it can be a real challenge to explain enough for the reader to understand the motivations, without lecturing. Dialogue can help, but a writer has to avoid one character stating the obvious to another. Keeping emotion high in the scene can help "research" seem more natural.
Trevelyan and Callie are childhood sweethearts with a taste for adventure, until the fateful day her father discovers them embracing in the carriage house and, in a furious frenzy, drives Trevelyan away in disgrace. Nine long, lonely years later, Trevelyan returns. Callie discovers that he can still make her blood race and fill her life with excitement, but he can't give her the one thing she wants more than anything—himself. For Trevelyan, Callie is a spark of light in a world of darkness and deceit. Before he can bear to say his last goodbyes, he's determined to sweep her into one last, fateful adventure, just for the two of them.