Allow your candle to burn for a minimum of 3 hours to create a full "melt pool" that reaches the edges of the candle vessel. Extinguishing your candle before the melted wax has reached the edges will create a tunnel down the middle and could result in lots of leftover wax.

Keep lit candles away from any draft or direct air flow (i.e fan, window, heating and cooling) and discontinue burning when 1/2 inch of wax remains in  the container.