Toss a hefty dollop of icing or whipped cream into the center of the cake. Using the back of the spatula, begin pushing the cream back and forth using short flicks of the wrist. Stop when the cream is about 1/4 to 1/2-inch thick. Rotate the cake by spinning the cakeboard, and continue until the surface is covered.
If making a layer cake, add the second layer; repeat. Don't worry too much about perfecting the top—for now, just be sure it's completely covered.
Alternative: Scoot the cake to the edge of the counter so one side hangs slightly over.
Using the back side of the spatula, push the icing around the sides, leaving about 1/4 of an inch all around. Grip on to the cake board to rotate the cake itself, not the spatula.
Add dollops as needed.