My reply is to pick a beginning >just pick one< Two of the people who approached me wanted to do something of a memoir, and in one case it was important to paint an early foundation behind a family relationship so that later issues would be fully understood. The other one, I think, simply wants people to understand him, and so a beginning might be kind of hard to nail down, but still, a beginning needs to be THE beginning - first thoughts - first realizations - first conflicts.
This holds for starting a fictional story too, no matter the genre you choose to write in. Pick a beginning - somewhere where the crux of the matter starts - somewhere where you first understand that a certain chain of events has come together.
I've picked several different points of beginning: A voluntary medical procedure which changes everything - a chain of deaths that forces my character to make hard choices - love at first sight - murder - the fall of the royal family, though my character did his best to avoid stepping into his responsibilities. Those are just a few, but you get the idea.
For me, starting a story was always rather easy. Some idea would give me a scene and then I would simply have a suitable character work out the details of getting to or from that scene. The biggest issue is agreeing on an ending. Sometimes my characters decide on something else, but it's still a goal.
Some people like to do a story outline. I prefer to drive in the dark with the headlights on high, but something of an outline might be useful as something like mini-goals to achieve within the bigger story. Whatever works for you, by all means have at it, but don't spend so much time on your outline that you get tired of the story before you start writing.
Recently I've offered my services for hire, but I do also try to be available just to help out. I do enjoy helping other writers however I can.
How do you come up with your beginnings? Inquiring minds wanna know.