Use the three reference images of clean line drawings and sketch them using simple loose lines.
Don’t try to match the cleanliness of these drawings. Instead, sketch them out with energetic, tapered strokes. Don’t hesitate. Just practice moving your arm with confidence.
If you draw some lines and then you realize that, Oh, shoot, I need to curve that more. Go ahead and just draw the new curve right over it.
As you get more confident that you’ve found the shape, you can darken those lines and the lighter lines start to disappear. Focus on the big idea and the shapes the lines represent, rather than on each individual line.
Good luck and please have some fun!
Example :
