Pipe the doughnut pan no more than ⅔ full. If the doughnut pan is filled more, the doughnuts will no longer have a hole once baked as the mixture will rise and fill the space.
Leave the doughnuts to cool completely before decorating. They cool pretty quickly, taking about 20 minutes or so. Doing it sooner could result in the buttercream melting, leaving you with buttercream soup instead!
When making the buttercream, beat the butter really well until it is really fluffy before adding the sugar. This will give you a light and soft buttercream, which is really easy to work with.
Likewise, give the buttercream a good, vigorous stir after everything has been incorporated. This smooths out any air bubbles, so you are left with a smooth buttercream to work with.
Pipe larger and smaller stars of buttercream over the doughnut or equal sized ones for different effects of the decoration of the wreath.