Susanna - from Santee, CA
First, make sure that your cake tiers are completely level (top and bottom) before you start decorating the tiers. Then, since cake does have a tendency to press down from weight above, when I cut my dowel rods which support the cake, I cut them just a bit shorter than the cake layer itself. That way, if I haven’t leveled the layers as well as I should have, the cake on top can “self adjust.” Finally, if I’ve done all these things and still have some small gaps, I fill in the gap with extra icing or add additional decorations at the space.