There are so many ways to begin. I'm starting something, and I approach it from mutiple angles, but here are a few things to zero in on:
What is the conflict? Conflict equals drama. Drama equals story you really want to keep reading (or watching.) Pile on the conflict in every scene. But figure out what the main conflict is. Are the Nazis butting heads with Indiana Jones to get the Arc of the Covenant? Voila, conflict.
Who is the protagonist? Who is the antogonist? Be sure to have one of the first, and at least one (if not more) of the second. In more literary efforts, the antogonist can sometimes be an internal struggle, an alcoholic tries to stop drinking, so their disease is the antogonist - that sort of thing. Or make your villain the Nazis. They're always good antogonists.
What does your protagonist want more than anything? This is a biggie and needs to be something vital, preferably life or death. Or at least your protag thinks it's life or death.
What does your protagonist need more than anything? They learn that they need something different than they ever dreamed. Like, the unpopular girl who just wants to be invisible in high school who gets the lead in South Pacific and learns to that she's got talent, and it's okay to be noticed. See how what she wants (to be invisible) is diametrically opposed to what she really needs?
Sometimes I lose sight of these central questions when I'm figuring out characters, day-dreaming up some cool scenes, or building my imaginary world. But if you can figure out the answers to these questions, your story will have heart and meat.