The first time you burn your candle, please allow it to burn for 2-3 hours to create a full melt pool.  "Melt pool" means that the melted wax reaches all the way to the edge of the outer area of the container.  This ensures a clean, even burn all the way down.  If the first burn is too short, the candle will only burn down the middle, creating a tunnel.  The wicks should be no longer than 1/2 inch.  Be sure to trim your wicks before lighting the candle.  Trimming your wicks before lighting will increase the life of your candles.  NEVER leave burning candles unattended.