If you plan to use your arrangement for a centerpiece, space your most eye-catching flowers evenly on all sides of the arrangement.
Continue placing your other flowers into the vase, along with any leaves and other filler material you want to use.
Cut your materials, as you place them, so that the overall shape of your arrangement forms an oval or a semi-circle.
If you need something to hold your flowers in place in the vase, you can buy foam or pins that are specially intended for that purpose from your florist.
Enjoy!
There are no absolute rules in flower arranging. The most important thing is to create an arrangement that is pleasing to the eye. The more you practice, the sharper your creative instincts will become! There is a lot of pleasure to be had in arranging flowers, as well as in enjoying the arrangement after it is done and in seeing the pleasure that it gives to others.