Don't overmix it

You should be careful not to over-whip your buttercream if you're making it expressly for a cake or other baked dish where the frosting will be on full show. If you do, substantial air pockets will begin to emerge, changing the texture. It goes without saying that you want some air in your frosting to give it a fluffy texture, but there is a narrow line between silky buttercream and one you can't smooth out.

You can remove the buttercream from the mixer when it has a spreadable consistency to avoid this icing error that everyone does. The frosting in the bowl should next be scraped with a rubber spatula to test the texture. If there is resistance, the scraping should continue for a little while longer. Do not worry if you discover that the frosting already has air bubbles in it; this is an easy repair. Simply smash the bubbles on the bowl edges with the same spatula to cause them to disappear.