Hi comrades!

i have few questions. i am trying to sit properly while i'm drawing but when i draw tiny boxes, i just bow toward my paper in order to draw those lines decently so do my back have to be straight all the time? or can i bow little bit to draw tiny detailed things? also am i allowed to use my elbow ( not with wrist) to draw short and straight lines like 2-3cm ( about 1 inch) because it is hard to draw those mini lines with my whole arm which has biggest Arc. or maybe i continue drawing by my arm for becoming proffesional artist?

also when can i move to next lesson?

Any Critique, Opinion & Tips Will Be Appreciated. Thank you

Sorry for my grammar :)