Biros or ball point pens should not just be the reserve of writing for they are great to draw with too. They move smoothly across the surface of the paper and are fairly quick drying. The fact that they can not be erased should be considered a benefit. Every mark will be visible so i recommend starting with a colour biro and make more marks than you need as you scribble out the form. Complete the drawing with a black biro but this time focus on the details and accents. You should end up with a lively little sketch.