Before I start, a disclaimer of sorts. I just want to stress that I am no expert in scribing and detailing. But I do have a certain level of proficiency that is good enough for me to get by. The tools and methods I mentioned below are derived from practice and experience I accumulated over the years. So it might not work for others.
When I started out in 2002-2004, scribing panel lines was unheard of. The first person who mentioned it to me was my Mentor, Leon Ku. He was doing it and encouraged me to give it a try as well. It was an interesting technique to me back then. Little did I know, our Japanese counterparts were already light years ahead of us in this department.
One of my first works where I attempted scribing, A mustard colored EX-S.