Some of your lines in the third section of exercises seem wobbly and unsure. Make sure you are ghosting your lines in one direction multiple times, until you're sure you have the correct angle, length, and speed before you place your mark for both your straight lines and your ellipses. This way, your lines come away clean and confident.

Also watch out for repeating or correcting mistakes, as drawing a new line over a mistake will only draw attention to it and make your work seem messier. When you draw a line with an incorrect angle or distance, just leave it be as if it were drawn correctly.

Keep in mind as well that adding subtle lineweight to the silhouette of your forms is a good way to accentuate the form and make it easier to tell the viewer it's orientation in space.