There is no hard and fast way or rule for how to begin your story. The best advice is probably, don’t begin at the beginning; which is great, if you know where the beginning is. Is the beginning when your character is born, in the manner of Charles Dickens? Is the beginning when your character dies? Is the beginning just before or at the point of the inciting incident of your story?
Begin Just Before the Action
Is the bus about to crash? Start your story thirty minutes before that. Is her husband leaving her? Start the story three days before he says the words she suspects are coming. Is he about to discover that he is the only one that can return the Axel to the Cavelon Dome? Start the tale before he is about to make the discovery.
This gives you time to establish the setting, introduce the characters, do what else needs to be done
Write One Sentence
When I put pen to paper, I like to begin with a sentence that will pull me in and move me along. Basically, it has to be a sentence that gives birth to another sentence. Ideally, your first sentence will trigger some form of curiousity in the reader’s mind and in yours.
So focus on just one sentence at first, don’t stress about the rest of it, because the rest of it will come if your sentence is doing its job.
Set the Tone
If you are writing a humorous novel, make me laugh or smile from the get-go; if your character is witty, establish his or her wit quickly; if your book is a fantasy, let’s see that in the first paragraph or two. Unless you are making an artistic choice, there is no real point establishing halfway through the novel that your tale is sci-fi. This will most likely annoy the reader, whether they were expecting sci-fi or not.
Get Your Characters Talking
This is a preference of mine, but it is also good practice, bring dialogue in early. The truth is, the days of Thomas Hardy and Charlotte Bronte are long gone, and few are willing to go through reams and reams of description to get to the heart of a story. Dialogue can place a reader quickly and expertly through accent, syntax and so on. Also, if you are unsure, giving your characters something to say can help you to understand your story a bit better.
Do I follow these rules all the time? Yes and no. This is what I do more or less, though I am not always aware that I am doing it. So let me know if it works for you.
Remember you don’t have to stick with where you started. If you are done with your story and a sentence in the middle seems like the better choice for your beginning, then by all means, move things around.