I think the most important thing is letting flow the feelings and emotions honestly.I feel good doing this.This good feeling within, I think , will create the habit to the journaling flow.
Actually, in the moment I'm responding this, I've just finished of journaling. I would say that the best way, it's just by doing it. Set an alarm and do it. It's a healthy activity that besides all the benefits, also bring you joy, it's entertainer and pleasant to do it.