Here are visuals to to help you learn the process...
BASICS:The first decision is where to place the drawing on your page. Lightly draw a very basic shape, or outline, on your page and you won't just be leaving the placement up to chance. For the daisy below, I drew two ovals, one defining the outside shape and one defining the flower center. Notice that outside oval is merely a guide, and many of the petals fall short of the perimeter while some might reach outside. The center oval is actually placed above true center, which allows the petals closest to the viewer to be longer.
FIND THE SKELETON:Plants tend to be organized in patterns, and when you can make sense of the pattern you can draw them. Generally, a good place to start is with the structure — that which connects or holds up the subject. Look for specifics — for where leaves connect to stems, numbers of petals, jagged or smooth edges, petals arranged in a circle, curves or cupped forms.
Look for what is "the rule" and also for exceptions to it.