One of the first issues to resolve in approaching an extended narrative is the focal points of story consciousness. The original story consciousness always resides outside the narrative, springing from the author writing the text. Some writers don't conceal this, presenting themselves as the teller of the tale, but most writers construct a fiction about who is telling the story, which we’ll call the primary story consciousness. The story is filtered through one or more of the characters, or being told by a witness to events, or being narrated by a central consciousness that knows all. Because events rise from this storytelling consciousness, it's important to figure out the source of the story at the very start. Begin by asking yourself who is telling the story. In first person narratives, the answer to this question is usually straightforward: the story is being told by the first person narrator. Third person narration is not as clear cut, springing from one or more characters; from a narrator who knows enough of the story to explore it but doesn’t know everything; or from a God-like narrator, who may be visible or invisible.
Once you’ve established who is telling the story, figure out the rules that the story consciousness must obey. The narration has access to the thoughts of this and that character, for example, but not those characters. The narrator knows the past but not the future. The narrator knows how everything will work out, or knows nothing. Define the limits of the narration and you'll see this eliminates problems with perspective shifts, because you'll build the range of narration into those first pages and not stray from that range for reasons of convenience.