Theory:

Diaries are wonderful objects that enable us to discuss the emotions, record dreams or ideas and reflect on daily life in a safe, private space. While there's no single, definitive way to write a diary, there are some basic tricks to be used to get the creative ideas. Even some inspirational quotes can help to get started on new entries.
 
The format of writing a diary is simple. It contains the following:
  • Date – Specify the date
  • Day – Write on what day the diary is being written
  • Time – Specify the time on writing the entry
  • Content – This is the main part of the diary entry, here write about the day or anything
  • Name of the person – The signature of the person can also be added along with the name.
 
Think about the following questions in order to have a clear mind before writing a diary:
  1. What was the important thing you wanted to talk about?
  2. Why is it important?
  3. Do you want to fix something?
  4. Why does it need to be fixed?
  5. How do you feel about it?
These questions help to make a plot which will define the diary entry.
Example:
1st, December
 
I want one of those summers that all the great artists write about in their lyrics. One that has a summer romance and friendships that I will never forget. Filled with memories that warmth my heart just thinking of about them. I'm waiting for the day to come.