To ensure that your candle doesn’t tunnel, the first time you light it be prepared to let it burn until the entire top layer of wax has melted across. Each time you burn the candle after this, it will burn evenly. This is also known as candle memory. If you extinguish the flame before the top layer has melted fully across, it will burn this way each time and the unmelted wax around the edges will create a tunnel, which is essentially wasted fragrance.
Always trim the wick
To prevent your candle from smoking, always trim the wick before each use. This will also keep your candle clean and free of residue.
Dip to extinguish
It always best to extinguish the flame by dipping the wick into the melted wax. When you blow out a candle, the wick continues to burn for a short while, causing it to smoke. Instead dip the wick into the wax to extinguish, and then pull back out so that you can light it next time. I usually do this with the end of a used matchstick, but you could use tweezers, or a blunt knife.