I am planning the placement of my roses to keep an softly oval shape.
Placing the outer roses first will maintain the final size of the bouquet.
Unless you want a tight, perfect compact bouquet, keep the design a little more open and loose.
Insert the flower stems in about an inch or so. Not deep enough and the flower won't hold fast into the foam. Inserting too deeply begins to cause the stems to clash and hit inside the foam and start to degrade the integrity of the foam.
Note the placement of the first three roses.
I'm extending the bottom right rose and little longer than the left bottom rose.
Note the placement of all four roses. All the outer roses face up or down and outwards.
I place the first center rose, having the rose face tilt up slightly upward.