Here's a general diagram of how I place my flower heads and how I decide on what direction each flower will face.
From the side view, some flower faces need to be facing to the sides because they are seen from the side. Remember - it's the bride coming down the aisle that gives the guests the first side view of the bouquet!
The flowers begin to cluster together - continue to add more into the design.
Carefully view the bouquet from all sides and fill in any "holes" you see.
I keep adding flowers and more seeded stems.
Your eyes are drawn (see the center?) to the openings where another flower is need.