There is no one-size-fits-all way of journalling, but I think one thing stands out: "How does the thing that I am writing about makes me feel?"
I think that is the most important question in journalling. When you confront yourself with a situation, experience or person by writing about it, you are basically investigating the emotions that are connected to them. Repression of these emotions is what puts your mind in a state of anxiety and what holds you back from feeling better, so what you try to establish is acceptance of those emotions. If you accept them, the brain will learn to no longer fear those emotions. How is that done? Maybe by crying your eyes out, maybe by slamming your fist through a door, but there is also the great technique of meditation. By just sitting with your emotions, noticing them, feeling them, without reacting or letting yourself be distracted by thoughts, sounds, symptoms etc.. Just do search on meditation. No need to buy incense and put on orange clothing, just sit down in a quiet peaceful location where you won't get bothered, close your eyes and focus on any emotions that were triggered by journalling. There are numerous guided meditations on the internet, just browse youtube and find one you like. Or if you hate hearing a voice telling you what to do, like me, just do it with some sea shore sounds or whatever that you find calming.
Be aware of any resistance while journalling. Resistance is a dead giveaway from your brain that there is something to investigate further, so don't let it stop you and journal further.
Also do not journal all day, one to two hours a day should be more than enough.
Again, go read the link I gave you to see what fits you best.
) . I feel journalling is a very important tool in dealing with trauma.