Writing a story is a fun creative outlet, and authors can use creative license to format their stories in various ways. One popular format for a story is a diary or journal format, in which the story is told through the point of view of one character writing his thoughts and describing events in his diary. A diary story should be told in first person and requires careful planning, as diaries can be too descriptive and lacking in action, which does not make for an effective story.
Brainstorm ideas for your diary story. The most important thing to do is to understand your main character who is writing the diary. Allow yourself to ramble freely in a notebook or document as the character, using "I" or "me" as if you are the character. Let him talk about his likes and dislikes, his emotions, his story. You may be able to use some of these thoughts later.
Write one paragraph summarizing your story. A diary story cannot simply be a collection of journal entries that does not have an actual story arc; like any tale, there must be a definite beginning, middle and satisfying conclusion.
Write an outline for your diary story. Focus on the main events that happen to your main character that he will be writing about in his diary, and write them in chronological order. Add any notes or bits of dialogue that occur to you as you outline.
Write the first draft of your diary story based on the outline. With any story, but particularly one in diary format, voice is vital if the story is going to be successful. The only way to find your and your character's voice is by writing regardless of whether or not you are happy with what is coming out. You may not find the character's voice -- his mannerisms, the way he talks and phrases things -- until the end of the first draft, but you will be revising and can fix this.
Include dialogue in your diary story. While most actual diaries do not include written out dialogue, a story does, and you can write dialogue to both enhance the story and make it more entertaining and believable for the reader.
Read and revise your dialogue story. Pay constant attention to the way your character writes and expresses himself, and edit or delete as necessary. While technically you can have intentional grammar errors in order to sound authentic, remember these must stay consistent throughout the story.