On the first burn, allow the candle to burn long enough to melt the wax from one side of the glass to the other. (This should be approximately one hour per inch in diameter.) This will keep the wax from forming a tunnel down the center of the candle.
Only burn the candle for 4 hours at a time.
Following these instructions will ensure a long lasting, evenly burning candle with very little wax remaining in the glass.