Candles will last longer (almost 2X), if they are placed in the freezer for a day before using them. Chilling the wax gives it a bit longer before burning through and leaving you with an empty jar. For some candles this will also cause them to drip less and burn straight down without burning through the side of the candle. Likewise, tossing them in the freezer when they've burnt through is a great way to remove the residual wax, as it should just pop right out!