The Principles and Elements of great design in floral art and flower arranging is finally now available in an exclusive CD, " Principles and Elements in Floral Design" with Ngaire Clarke. Try a lesson on each element and principle with a floral project to try, read more here. The feature illustrated here is pattern

That means, simply, repeating what you did several times, to make a pattern.
On the right, pictured in Melbourne Australia,is an excellent example of  pattern The geometric lines and forms of this design, which can characterise 'pattern' are further enhanced by the way the blocks are placed. This makes an interesting silhouette to provide variety and gives the whole design more 'personality'.

Compare this to the picture of the design below it, also from Melbourne, and  you can see it is less interesting, with less need for your eye to rest on the design for long.

Therefore if the outline of the final design is important, the overall shape should be interesting .

This massed display  pictured on the left, uses pattern as the  main design element. The overall shape of a cone is further enhanced with a top of huge rolled leaves and linear plant stems to provide contast with line, add space, and give an interesting silhouette.