To start with, I lay down some ellipses to establish cross-sections along the length of our mushroom's stalk. Being that this is very much like a cylinder, the same principles do apply. For example, we certainly would benefit from aligning these ellipses to a single minor axis line - and if you struggle at all with keeping them aligned to each other, I would definitely recommend this.
A less optional point to follow is the fact that the degree of these ellipses shifts visibly as you move from top to bottom. The topmost ellipse is more in line with the viewer's eye level, so we see less of its surface. As the cross-sections move further down, the angle at which we see it becomes greater, resulting in more of that surface being visible to us.