Here are a few ways to properly burn a candle to maximize the duration and scent throw:
Trim the wick
The ideal length for a candle wick is one-fourth of an inch, so make sure to trim the same to this size before actually lighting the candle. If it still produces soot, trim it even further until you get a clean flame.
Make sure the candle size and type is appropriate for the room.
The candle size should mimic the size of the room. Large candles with two or three wicks produce larger wax pools, which create the scent throw. Medium size candles (7-10 oz.) with one wick are appropriate for a medium-sized room, such as a bedroom or a bathroom. And small candles (2-6 oz.) are only capable of scenting a small room, such as a bathroom or entryway.
Burn the Candle Longer.
Let the candle burn at least until the wax pool reaches the edge of the container (or about 2-3 hours after lighting). Blowing out the candle before the wax pool reaches the edges will produce "tunneling," that pesky issue that causes the wax to create a tunnel inside the jar. The tunnel is essentially wasting the wax that remains on the sides of the container.
If the candle's wax pool isn't quite reaching the edge of the container after about an hour (for a medium-sized candle), try swirling the candle container gently to encourage the wax pool's reach.
But Don't Burn it Too Long.
Extinguish the candle when the burn pool is less than 1” deep in the container. Burning the candle longer will heat and evaporate the fragrance too quickly and weaken the scent throw over time.