When writing a historical novel—fiction, romance, biography—ensure your names, events, and facts are accurate when you referring to real-life people and occurrences. Otherwise, for those in the know, you may evoke some [hysterical] laughter.
Determine the period and consider the POV you’re going to use. What’s your starting point? Will the main characters be fictional ones or real people? Perhaps a combination? What about the plot? Will it revolve around real events or be fictitious ones (with real ones, possibly, as the backdrop)?
Make certain towns and cities, and the like, are spelled correctly. Dates, if used in conjunction with actual events, should be accurate. Ensure you depict details precisely in and around the storyline and characters.
Become familiar with the various components of the time:
** incidents (wars, inventions, discoveries, explorations) ** fashion/clothing (for the rich and poor) ** customs/etiquette (for the rich and poor) ** social norms ** technology/art/culture ** expressions and vocabulary (in the 17th century, people would not say things like “that’s so cool” or “butt out” or “text me”) ** beliefs and principles.
You may not necessarily use all the information, but be familiar with it; it will help you paint a more vivid picture. And the more vibrant, the more exciting . . . because that’s what you want . . . to excite your readers and have them return for more.