Leave plenty of time when you’re burning a scented candle for the first time. If you blow it out before the wax has ‘pooled’ all the way across, it will continue to burn down the middle and not melt the wax at the edges. (It’s called ‘tunneling’.) Also: we’ve learned the importance of making sure the surface your candle’s placed on is completely flat – using a spirit level – or again, it can burn down one side and leave the other solid. (Such a waste of a wonderful smell!)