The technique of the ball point pen is to create small, light, one direction lines ( no zig-zag), on paper, and then to do that in multiple directions if we need to shade. Imagine toilet paper. The better the quality, the more layers it has.
Same principle here, we start with a "mesh" then add another then another.
The great thing about ballpoint pen, is that it has vibrant colors that give a comic-book/illustration look to the drawing, making it spectacular, but the inconvenience is, that there is no room for mistakes.
This is why I strongly recommend to try this method once you have mastered the graphite drawing.
Remember to be light on the paper, it is all in the movement of the wrist, while you turn your subjects
.