If you knew a story you were writing would reach a huge audience, what would you make it about?

about real life complications and issues... something realistic not imaginary or fantasy.

A writer has to keep his fingers on the readers' pulse. Knowing about your audiences helps. If you write about issues - even in creative writing - that are not relevant today...you are likely to have a dearth of readers....if you write about current issues in vogue......you would be ensuring vast readership. 

As a creative writer, I don't go after the number of people to reach.  Rather, I write what would be significant and appealing to the readers.  And these are two different issues. Writing for the sake of targeting as many readers as can be would kill my creativity; and the result of my work would not be very good.