Freeze your layers after cutting and before frosting -- this keeps the cake from getting as crumby when you frost, and it makes it less likely to fall apart as you handle it. Wrap cooled cake layers tightly in plastic wrap and freeze for at least one hour.
The trick to a prettier layer cake is starting with even layers. To ensure even layers, let your cakes cool out of the pan. Use a very sharp serrated knife, and go around the edge, slicing only an inch in. Once you have the edge fully cut, finish slicing into the center.
Buttercream is the easiest frosting to spread and it's ideal for intricate decorations. For a more forgiving -- and less rich -- option, use seven-minute frosting. Similar to a Swiss meringue, it uses only egg whites and sugar and whips up into an airy, ethereal mound, making even the most rustic and messy application gorgeous in a rumpled way.