Determine the characters that you want to tell the story through. Although the narrator is independent of the characters, if you need the narrator to follow multiple characters, it will affect future decisions on narrator omniscience.
Decide on the omniscience of the narrator. This can be omniscient, where the narrator knows absolutely everything and can describe the thoughts of any character in the story. An omniscient narrator can describe any scene in a story and can even jump between character heads in a single scene. The narrator can also be objective, where he can follow any character, but can only describe events. An objective narrator cannot get inside character's heads and describe thoughts or emotions. Finally the narrator can be subjective, where he knows everything, including thoughts, about just one character.
Write the events in the book, following the characters that you need to and using a consistent level of narrator omniscience. Refer to characters by name or use pronouns such as he, she, him, her, it or them. To prevent shifting your point of view during the story, never use I or you as subjects in a sentence other than dialogue.