Thank you! I´ll upload some more soon to show some other approaches and techniques.
@Crucent: Never mind.^^ I always try to draw a line in one quick stroke to make them clean and dynamic and to get that marker-like look. I flip or rotate the canvas to make it more comfortable for my hand. Sometimes I need to repeat until the line pleases me.
@Embala: I know what you mean. I always watch other artist´s videos with open mouth. One can only watch the technique, which is quite simple in most cases, but to handle it properly it takes years and years of practice (in my case, it took 20 years), and massive background knowlege about surfaces and solid figures (like spheres, cubes, etc.) and their behavior in a three-dimensional room, especially when it comes to shading.