I write historical romance and have learned a few things along the way, but there is always more to learn.
Write what you know and love. When I started writing there was really no question for me that I would be writing historical westerns. I love books on highlanders and stories about pirates but I do not know the history well enough and the brogues and societal things weigh too heavy for me to study all that. But cowboys I knew. That being said I still have to do my research on each story.
The first thing is to make sure to do your research. If one thing is off even a little, I promise a reader will point that out to you. It will be necessary to know the era, time period, living style, conveniences, language and dialogue, dress, foods, method of cooking, etc.
When doing research use sites that really offer you the true history. For detail Wikipedia might give you some insight but I will bet you can do better. So did in. Check out the Library and related books.
Reading stories in your same genre is a good start too.
If adding a piece of true history to your story, read up well to make sure you have it right. But it might also be good advice not to add too much historical facts until your story feels like an encyclopedia.
Give your characters relatable struggles for the time period.
Be careful to be respectful. I tossed a Cheyenne Medicine Man into Dawson's Haven and I had a lot of American Indian traditions in that story and the story I am not writing for Leaning Bear called Paint the Sky. The issue is while I did a ton of research I am still not sure it is all perfect and my aim in the story was not to offend anyone. So I had my editor let me add a small paragraph about trying to depict true history and that I might not have it right but that any errors are completely my fault and not mean to be negative toward any of the tribes. Something like that.
I am guilty of having to watch not to toss in modern terms. I have to sometime look up the history of a word to see when it actually came to be in use.
And no worries like I said, some reader will point out for you what you didn't get right. I usually answer rather generically. "Thanks for you comments, I do hope you enjoyed my fictional story." (Bite me!) Kidding but seriously it is best not to haggle as everyone has an opinion and authors are human.
Rule of thumb, if your mind questions it, then look it up, the reader will too.
