Another great florist tip is to pay attention to the angle when inserting flowers into centerpieces. Flower heads grow towards the light, thus many times the neck is bent naturally.
Use this to your advantage when designing your centerpieces. Here, I'm placing this mum in the bottom, with the head facing upward.
That way the flower head is facing in the exact way I want it to be seen. Pay attention to the natural way your flower heads lean and curve and work it into your overall design.