The shape of the ellipse of the outer edge of the cone and the location of the flower bottom are the two most important reference points to catch in your preliminary sketch. This fairly stiff demonstration emphasizes the geometry of the shape. Keep these steps in mind when drawing a real flower. This framework will help you capture the geometry of the flower. On top of this you can add the individual character and twists of individual petals (a topic for another blog).
Click on the first image to start a step by step slideshow.