When lighting your candle for the first time, make sure you wait until the wax has melted evenly across the candle. By ensuring the whole surface has melted before you extinguish your candle, you'll avoid tunnelling and help your candle last longer.
Burn your candle for 3-4 hours at a time.
While you may want to burn your candle all day long, to ensure your candle lasts as long as it can (40-50 hours), make sure you don't burn it for longer than 3-4 hours at a time. However, if you do choose to burn it for longer than that per session, all that means is you'll get to buy a fresh candle a bit sooner.
Trim your wicks.
Before re-lighting your candle, make sure you trim it to a 1/4 inch to ensure the smoothest possible burn.