Wiring your button mums by gently inserting the wire parallel to the flower stem and inserting upwards so the tip of the wire is buried in the flower head. Tape down the wire stem.
Try to keep your stems slender and smooth, to create as small of bulk as possible.
On cushion poms (or Viking poms as shown here) you insert the wire up the stem and up thru the center of the flower head.
Bend a small hook at the top of the wire and pull down gently, burying the hook into the flower head.
I usually wire all my flower heads and greens at the same time. It makes your assembly time faster.