First and foremost I learned how to make icing:
beat together-
1/2 cup softened butter
1/2 cup crisco
1 tsp. vanilla
gradually add-
4 cups powdered sugar
then add 1 tbsp milk more or less if needed.
To be honest I personally don't like the flavor of this, it just works really well for decorating.
One of my biggest challenges with cake decorating was that I could not use butter, margarine, shortening, or milk. I pretty much only had rice milk to work with and I couldn't make it thick enough. But I have since discovered a soy-free shortening and margarine and I think I will be able to do this now!