Go to any writing class, and they tell you have one page to grab your reader. Some will even advise that it is the first line that tells whether or not your reader will continue reading. That's a little intimidating....or challenging, depending on how you look at it.
Fiction writing books will tell you that the first line must introduce the character, and action, and emotion. One of my favorite first lines comes from a novel by Julie Lessman entitled A Passion Most Pure. It begins, 'Sisters are overrated.' That's a fantastic first line, and the rest of the book didn't disappoint.
Feel free to leave the first line from your current work in progress, or a favorite first line from a novel you are reading in the comments section.
Happy Writing!