I tried to index my journals, to collect the principal ideas, to recognise themes in my work, and that was useful to me, but it was still dealing with ideas at a distance. I needed to become intimately involved with these themes, and not deal so much with what should be, but deal more with what I intend to do. There was no easy route to this integration except by my own effort using the tools I chose. For me the journal was a principle tool that allowed me great insight and gave me increased personal confidence. I could have achieved that objective much earlier if somebody had been able to instruct me on some more efficient techniques.
Good mentors are few, mentors for journal writers are rare.
If you have major areas of interest it may be useful to open two or three journals so that related material is kept together. It would seem easy to separate business matters from personal matters and from your interest in medieval history, but in fact you will find it requires discipline. If you want to write down an idea the journal you need usually seems to be at work or in the car. While indexing your journal as you write it would be time efficient, I find that difficult. I usually date and source items as I start to write, leaving space for a title.