At the very beginning, gain knowledge about script writing and narrative techniques. You can analyze movies as you watch them - pay attention to dialogue, to characters and camera shots.
Also start watching tutorials on the subject or reading articles and books.
In addition to the above, you should have inspiration and a positive attitude.
You can create an environment around yourself that will give you the mood and inspiration.
If you want to create war-themed movies, you can review your favorite war movies and try to feel the narrative that the author was going to convey.
If you want to make a film about romance, or about love, you can create such an environment around yourself. If you have a girlfriend, you can ask her to help you create such an environment to write a masterpiece.