Writers are often told to start with action. This is early writing advice, to get you past beginnings on the first day of school, as someone wakes up, staring into a mirror, recounting family history, etc. But you can't swing too far on the pendulum. Start me off with a plane crash where only your main character survives, and I'll mourn the dead. Start me off with your main character's actual life (with movement toward goals, which may be a better term than action) and then I might care more about him or her than the other passengers on the plane.
I would say don't start with Michael Bay, exploding things action (unless you're writing Transformers 7). Start with forward momentum. Start with building tension. Start with Harry Potter trying to get out of the cupboard under the stairs, Mrs. Frisbee feeling her son's forehead for fever, the rabbits in Watership Down staring at a man-made sign and wondering what it foretells. Then move to Hagrid's Apparition, Mrs. Frisbee's desperate appeal to Rats of NIMH, and the bulldozers destroying the rabbit warrens. Analyze the beginnings of your favorite novels and movies. There's a very good reason FINDING NEMO doesn't open with Nemo's disappearance.
I'm not sure if these are actually Pixar's rules, but they're great guidelines anyway. Once upon a time, _____. Every day, _____. Then one day, _____. Don't skip the "Every day" part. As I've heard it phrased before, tell me what makes your main character different from everyone else. That's the first question that should be answered, in my opinion.