For those who want to write non fiction, and I love writing about history, I would say make it interesting. History in writing should be as exciting as it is in action.
One way of doing this, is to tell a story. Instead of saying Teddy Roosevelt charged San Juan Hill, you could say it this way. The determined citizen turned soldier, albeit an unlikely mounted hero, climbed towards victory. Just because it actually happened, doesn’t mean it can’t be told with style.
Second, don’t only double check the facts, but research the small details. One seemingly insignificant point, can be the jumping off spot for your historical project. Something as simple as what Lincoln ate before Ford’s Theater, can open a whole new way of telling what people think they knew.
Third, avoid trends in historical writing. For example, when I grew up, I was blessed to be in the era of biographies being inspirational. Over time the trend shifted to uncovering every wort someone had. Resist the pull to write to a pattern, allow your individuality to show through.
Fourth, I would encourage you to be kind. Remember, this isn’t a fictional character. This was, or is, a living breathing person, with people either related to, or inspired by them. If you can find something positive in your story, share what elevates, inspire your reader.
The most famous historical novels don’t sound like everything else, because they’re not. Tell what really happened, get the details right, but showcase the unexpected. Avoid the common traps, and be kind. You may find that someone else’s history, is your masterpiece.