Do you keep a personal journal?
Yes. Org-Mode+Org-Capture
If yes, do you find it useful?
Yes. There are many advantages to keeping a personal journal. It allows you to have better recollections about what actually happened in the past, which is important taking into account that memory is constructive and prone to distortion. Many ideas and insights are forgotten, recording them is a way to fight that.
What tools would you recommend?
Emacs and Org-Mode. Git. Markdown and any other editor is a good option also.
Is there any specific methodology that you follow?
I use some ideas from GTD. Explaining my whole methodology would take more time than I have right now.
When journaling, do you try to track any specific aspects of your life or just write about anything that is currently occupying your mind?
Both.
Any advice on how to get the most out of personal journaling?
Make it an habit. Put a time or word limit and just let the words flow. Make it seamless, for me capturing an entry is pressing 3 keys.