One issue that commonly plagues writers is where to begin a story. The standard advice of beginning when the action starts or to start with an action scene doesn't always lead to good results. I will attempt to put down my thoughts on the subject in a way that I hope will be helpful.
The good news is that you don't have to find your beginning when you start writing. Sometimes it can be more helpful to your overall story if you go back and fix it after you have the ending to your story ironed out. For those who outline in depth, you might just have enough of your story before you begin your first draft, but getting in and writing it might still give you cause to go back and edit your beginning later.
The trap many fall into is equating staring your story with action to starting it in the middle of an action scene. That is the wrong sort of action. It might work for some stories, but for others it can set a incorrect image of the story. If you aren't delivering hard hitting action scenes all through your story, you probably don't want to start with one. No, the meaning of starting with action is to start with your first character doing something. It's supposed to be an action verb, not an action scene. It doesn't matter how mundane it is, but the verb should not be static. Looking in mirror is not action. Lounging in bed is not action. Driving is, opening a door, even waking up or some life event works. Visit your favorite books and see how they start. Chances are it isn't with a fast paced action scene.
What is that moment that is the best beginning? It is the moment when things change. It could be as seemingly insignificant as a blown interview or cancelled appointment or as eventful as a birth, death, marriage, or car accident. Think about it like alternate realities. What is the point where this story breaks off from all possible other stories. Then find the first interesting thing that happens. Often the very first scene will be the change, but at other times, it has already happened. Such as a couple agree to sell their house and move, but the first scene is their final walk-through of the house - the moment that sale becomes final, at least for the characters if not the bank. In the first Star Wars movie (Episode IV) the pivotal moment is when the plans are stolen, but it doesn't impact our characters until Leia gives the plans to R2-D2 during the epic battle over Tatooine. In The Hobbit, that moment is when Gandalf chose Bilbo to be the fourteen's member of Thorin's party, but we don't start the story until Gandalf puts a mark on Bilbo's door on the day of the gathering. And this is nothing new. Jane Austen started Pride and Prejudice with a conversation about Netherfield Park being rented at last, the day Elizabeth Bennett learned of the event that would change her life.
Also, if you like to be a bit more realistic, sometimes those early moments on the path to the conflict are not always that interesting. Maybe the key moment happened some months ago, but only now do things that make for a good story pick up. The key is to know what the pivotal moment is and how your characters get involved. One way is to have the opening scene be when another character gets involved. George Lucas used the two droids as his vehicle for moving the story. They are technically secondary characters, but they are the story link between Leia and Luke.
Once you lock in where to begin, the question becomes how to begin. That really depends on your story. But no matter what the story, you have to keep in mind two things. First, get the reader's attention and get them hooked by your story. Second, every story should build to the ultimate climax. You don't want to start with something so big and epic that the rest of your story can't live up to it. Now if you are going to tell a big epic war story, like Star Wars, you can start with a battle. If your character is in the military and a particular battle is crucial to the start of his story, then that works. What you don't want to do is make the opening scene bigger than the payoff later supports. You don't need big to snag an audience, what you need is something intriguing. Something that catches their interest. Movement and action verbs are just one of many tricks to do that. Mystery is another.
Like with just about every aspect of being a writer, the best education is to read and read widely. Step out of your comfort zone. Say, like me, you love science fiction and fantasy. On occasion, pick up a historical fiction, a mystery, a spy novel, or a chicklit. It will enrich your writing and let you in on what other types of writers are doing. I've found some pretty great books that way. While reading for enjoyment is always a good thing, as a writer, you really need to do more. You need to pay attention to how the plot unfolds, where they start the story, how the opening scene catches you, how the conflict builds and morphs and moves to the climax. There are many ways to structure a story and the more ways you know, the more widely you are read, the more depth your stories will have.