Research takes a lot of digging: on the internet, personal interviews, books, journals. You can compile a good deal of disparate bits of knowledge for a story, especially if you are writing an historical story.
All that digging is great. You have a real sense of the time and place. However, many first time writers feel that somehow their readers need to know how much time and energy you spent getting the facts. Well, I hate to disappoint you but readers and viewers don’t care about your research. They want a good story.
Joshua pulled on the reins as he topped (insert obscure mountain in Colorado) peak. Rain dripped from the fringes of his capote and he shivered. The sunset cast a pink glow on the towering snow capped mountains around him. He turned in the saddle and reached into his blanket roll where he kept his (insert appropriate hunting knife) safe from the rain and damp. Beneath his capote his buckskins stuck to him. It reminded him of the time when he was a boy in Boston when his mother set the entire (insert appropriate poverty stricken area of Boston for year 1846) astir with her (insert appropriate inappropriate female attire for 1846) and how he had lost his sweetheart Emily through embarrassment when John Watkins (never mentioned again in the story)…
You with the story yet? Yep, all those details can fit in but not at the beginning and you will probably leave out 80% of all the details you know from your research. If you give us historical details and back story about your protagonist you lose your audience. And that first audience may be an reader/agent.
And, please, no gratuitous sex just to show that people then had the same proclivities. Domineering, kinky, same gender, whatever—if it’s not integral to the story don’t do it. Gratuitous sex is not hip. Unless your readers are 12-14, they will be bored.
Using flashbacks at the beginning of a film script will give your audience the same ho-hum feeling. Cut.
Joshua’s horse stumbled as they topped the next peak. His own breath puffed clouds in the freezing rain, but he had to get to Jim Bridger before the pass was completely iced over…
OK, I’m over-dramatizing but the point is important. The story comes first.