Ballpoint pen technique
The technique of the ballpoint pen is to create small, light, one-direction lines (no zigzag), 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 a 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 trying this method once you have mastered graphite drawing.
Remember to be light on the paper, it is all in the movement of the wrist, while you turn your subjects