There are a few tricks for smoothing out buttercream. One trick is to melt a small amount of it (just a few tablespoons) in the microwave and add it back into your bowl. This will make it easier for you to work with it. However, doing this too much could make it runny. Another simple trick, as mentioned above, is to use a spatula to push the frosting to the sides of the bowl after you've made it. This process reduces air bubbles in the frosting, which can make it appear torn, scraggly, or a bit rough. Using a spatula to remove them will create a silky texture. I recommend doing this for a few minutes after you've made your frosting. Depending on when you're frosting your cake or cupcakes, you may want to wait and do this right before you plan to use the buttercream.