3 things I always do when stacking cakes:
1. Make sure the cake layers are level before building each tier. This means using a cake leveler, mine is a simple wire one that cost $4 at Michael’s, and I couldn’t live without it.
2. Punch a hole in each cake board right in the center with an apple corer, then wrap it in saran wrap. This prevents any soggy, wilting, tilting boards and allows you to easily put a small dowel straight down the center of your cake after the layers are stacked.
3. In each tier that you stack on, use at least 4 supports in the tier that are the EXACTLY the same height, measure them after you frost the cake. Regular drinking straws work perfectly. For larger cakes I use Wiltons Cake Straws. They are about the same size as PVC pipe which can also be used but it is more difficult to cut.