The first step is to find a journal that you will enjoy writing in. This can either be with an actual physical journal, or on a device if that is what you prefer, though, I recommend an actual journal of some kind. This is very important, as if you do not like what you are writing in, it is very likely that you will not enjoy writing in it either, and you probably won't.
The next step is to find some time to be alone, and a place you can be alone and uninterrupted in. Since journaling is a very personal practice, one where you are getting out what ever is on your mind and what ever you are feeling, it is recommended to find a very private place where people will not bother you.
Now, it's time to actually write. You can start writing, literally, what ever you want. I like to ask myself why I am even journaling, and to write that answer down. That question usually leads me to further questions. Find what works for you, ask different questions to help get your thoughts going, or, if you are having a bad day, write about that. Try to explore the things you are writing down, what they mean to you, your reaction to them, and anything else that you feel and that is in your mind.
It is important to understand that journaling should not be forced. You may find that sometimes, you will sit down to journal, but won't actually have anything to write down. What many people do in this situation is to force themselves to come up with thoughts to write down. This is not an efficient way to approach journaling, as you can get very tired of this practice very quickly.
You do not have to journal every day, and you do not have to write a whole page each time. Even the habit of sitting down and taking out your journal can help get you in a better mood. If all you have to write is "I had a good day", then that is all you need to write.
