Simple wedding centerpieces like these are made in a trough container (that means long and rectangular). You need to be sure to choose one with a liner so it doesn't leak out on your wedding tables.
You will need:
Float soak your Oasis foam in water treated with Crystal Clear Flower Food. Cut the foam to fit into the rectangle container. Cut laterals off the leather leaf fern and green up your container. (If you need more design help, check out the step by step flower tutorials in the Centerpiece Gallery.
Cut off your daisies and insert them in a long line down each side of the container.
Mist well with Finishing Touch or Crowning Glory flower sealant. Don't allow the foam to go dry. Keep in cool dark area until wedding day.
Here's the same look, but using standard carnations instead of the daisies or pomps.