Cupcake Swirl like a Pro

Smooth: Place a generous dollop of frosting in the center of the cupcake, then use an offset spatula to spread it across the top, working your way out to the edges. Once the frosting is evenly distributed, use the spatula edge to smooth it over the top and around the sides.

Simple swirl: Use a pastry or ziplock bag fitted with a large plain piping tip. Place the tip in the bottom of the bag (snip off one corner if using Ziploc), then use a rubber spatula to fill it about two-thirds with frosting. Place the cupcake on a flat surface and, starting at the outer edge, carefully pipe a circle around the cake, coiling it until you reach the center. Once you’ve reached the center, stop squeezing the bag and pull it away form the cupcake, twisting your wrist as you do. This will give the frosting a perfect center swirl.

Decorative swirl: For a more structured and finished frosting swirl, use a star tip to pipe. Use the same process as with the plain tip, and make sure to work slowly and carefully so you don’t disrupt the pretty pattern of ridges created by the piping tip.     

Quick tip: Don’t have an offset spatula in your kitchen drawer? A butter knife will do the trick.
by-http://www.allyou.com/food/cupcake-frosting-tips-00400000059980/