It’s been said many times that writing a novel is a bit like driving at night without your brights on – you’ll get to your destination eventually, but until then, all you need focus on are the events that are within your little illuminated sphere.
Writing a long work has another important similarity to driving at night – if you don’t know where you’re going or what road signs to look for, you’ll likely spend a lot of time completely lost. Before you begin a larger work, it’s important to give yourself a sort of ‘road map’ reminding you where you need to be at which points of the narrative. Drafting a synopsis or a chapter-by-chapter summary of your story is an important step toward completing it.
Your synopsis should give you a general idea of what your story will be about and which events will move your narrative along, but it does not need to be meticulously detailed. In many of my synopses, for example, my characters are referred to by nicknames like Cupcake or Adventureboy, and the phrase “they do stuff for a while I guess” pops up like toadstools in a manure pile. Save the specificity for when you’re actually composing the story; leaving out all but the largest of details will help you work more efficiently and make it less heartbreaking to change parts of your plot that don’t make sense when you look at the big picture of the narrative.
A well-written synopsis is like an artist’s sketch of a model or a landscape. It doesn’t give you all the information that will make up your narrative, but it at least shows you where this information will be. This makes it easier to get started on a long work and focus on your writing instead of where you’re going next.