Like a good narrative, the book cover and title should draw the readers' eye to it and engage and tempt them to pick up your book and invest their time and money in the story.
Interruptions! Being interrupted can be maddening for a writer. I need silence to write, so any noise--a ringing phone, or knock on the door, or somebody talking--discourages and yanks me out of my headspace.
Characters! If you do not have appealing, three-dimensional characters peopled throughout the novel or short story, readers will not care one iota about it. Good characters ground the story.
Set goals for yourself and stick to them! Carve out a chunk of time during the day, whatever works for you--maybe it's early in the morning, or late at night, or an hour in the afternoon. Write what you can--a paragraph, a page, ten pages--but write every day to keep the momentum of the narrative.