Sketching, sketching basic things and trying to understand how to construct rounding at corners of shapes. Here you can see my sketches and a construction of rounding. I usually draw with a pen or a fine liner because it makes me think and concentrate more on a sketch. You can’t erase these lines and it teaches you to be more careful and precise.
It wasn’t that easy to construct rounding, but it will get better with time – I just need to practice more.