You begin to get into the rhythm of working with both the flower heads and the glue. Practice makes it easier as you go along!
Some designers apply all their glue and allow the flowers to dry stem up then attach them to the design. I prefer to take my time and glue the flowers one at a time.
There is some leeway when the glue is still soft to adjust the positioning of the flower heads.
As you can see, I have formed a triangle of the three fully opened roses in the center of the glued leaves.