When making your bouquets, put the first flower in the middle and set it at the height that you want your arrangement to be. Then put the flowers on the sides as wide as you want the arrangement to be. Then add some filler and greens. You now see the basic shape. Then fill in the space with your main flowers.
Wiring refers to two techniques.
The first is where the wire substitutes as the stem. The natural stems are cut off and wires are inserted into the base of the flower, folded over to form a hairpin, and acts as an artificial stem. This is done so that you can have large bouquets yet a thin handle. The disadvantages of doing this is that as the flowers have no water supply, the work must be done very last minute. The second technique that goes by the same name refers to wrapping a wire around the stem of flowers so that even if the flowers wilts, the wire will hold it up.