Writing is a process of personal expression. Everyone does it differently. The best way to find out how to write is to have a go.
It's very important not to judge yourself as you write. Although writing is an act of communication, it is a private process, and your writing will not be judged or seen by anyone else unless you publish it somewhere. At its core, writing is a private process of contemplation.
This means that the most important thing is not to consider your audience but to establish a dialogue between the different parts of your consciousness as they collaborate to get words on to the page.
There is plenty of evidence that writing is a natural, healthy process and that it is good for the mind.
Pennebaker, James W., and Janel D. Seagal. "Forming a story: The health benefits of narrative." Journal of clinical psychology 55.10 (1999): 1243-1254.
Burton, Chad M., and Laura A. King. "The health benefits of writing about intensely positive experiences." Journal of research in personality 38.2 (2004): 150-163.
Lyubomirsky, Sonja, Lorie Sousa, and Rene Dickerhoof. "The costs and benefits of writing, talking, and thinking about life's triumphs and defeats." Journal of personality and social psychology 90.4 (2006): 692.