One of the secret rules of baking is and has always been not to skimp on the butter. Let the people you're baking for worry about their waistlines -- your job is to make fluffy frostings and delicate cakes. And for that, you're going to need plenty of rich, creamy butter.
Butter is something a good kitchen should never run out of, so buy your butter in bulk and keep it frozen. Transfer it into the refrigerator the day before you need to bake with it, and the butter will thaw overnight. Also, make sure that when you refrigerate butter, it's tightly wrapped and kept away from other foods, especially smelly ones. Butter will absorb the smell of the foods it's stored near, and nobody wants to taste leftover tomato sauce or hot dogs in their cookies.
Many holiday baking recipes call for softened butter. Microwaving a stick of butter is tempting, but that can make the butter separate too quickly. If you're not melting the butter outright, it's best to avoid the microwave. Butter will soften on its own if left out at room temperature for about an hour. If you're in a hurry, cut the butter into smaller pieces, and it will soften faster.