The key to a perfect drip on your cake is the consistency of the ganache, which is easily affected by temperature. If your ganache is pouring down the side of the cake and pooling at the bottom then your chocolate is too warm. Give it a minute to set and cool slightly before pouring it over the cake. If the ganache is too thick and not running down the sides then the chocolate is too cold. Give it a quick burst in the microwave for about 10 seconds to warm it back up.