Tuesday Tip: Wet Your Whistle.
Adding even a tablespoon of milk, water, liquor or fruit juice to frosting might seem useless but it actually improves the texture and makes it easier to pipe or stick to surfaces. Dry frosting can easily fall from where it's placed like the side of a cake or a piped border.
A lot of people, including myself, have skipped this part of the recipe in order to keep the icing nice and thick, but don't overcompensate and add too much. A little bit of liquid goes a long way!