Marilyne Mitani has used a myriad of garnishing techniques since becoming pastry chef at Danville's Bridges restaurant in 1997. Yet she's careful to not sacrifice taste for beauty. The flavor has to be an integral part of the dish. I try to stay away from putting mint on everything. This doesn't mean you have to use fanned strawberries on a strawberry dessert.
Contrast is preferable, as long as the flavors work together.
Pavlova she is offering tonight. Think texture as well. Crunchy bits of toffee might be just the thing to accent a smooth mousse cake, but powdery sprinkles of that toffee might be more appropriate if the cake is already filled with whole macadamia nuts. Some dishes have good looks and contrast built in, as with sesame-crusted salmon served with smooth carrot mousse. Buy a cheesecake or chocolate cake from a professional and save your energy for even lustier pursuits.