This type of flower head has a somewhat complicated pattern and is made up of several smaller florets. One should look more to getting the smooth curves of the stems and understanding and depicting the general growth pattern than in getting the details of the petals right.
Ascertain at first accurately the length and width of the flower and its general shape : circular, elliptical , conical etc. Mark the half way points and quarter points in your drawing, you can do this on the flower itself with a marker or with small colored tapes so you don`t lose your place when there are too many petals on the flower. Fill in the petals or florets between these positions: