Yeah, the best article I have seen is in Michael's web site. Unfortunatelly DBI is one of those techniques where you just have to do it and gain the experience by doing. If I recall correctly there is another good article in unlinkingeye, but I am not sure.

Some people turn film around and check the back, you can "see" the outline of the highlights, some people lift the film to view against the light and use a finger next to the highlights to judge highlight density, is up to you which way to use. I use both, depending on the negative.