1. You fall asleep with your candle burning.
What you're doing wrong:
First of all, never leave a candle burning unattended! If you burn your candle for more than 4 hours at a time, carbon will collect on the wick, and your wick will begin to "mushroom." This can cause the wick to become unstable, the flame to get too large, your candle to smoke, and soot to be released into the air and around your candle container.
Solution: Don't burn for more than 4 hours at a time (or unattended)!
2. You get a new candle on your way home from work. Yippee!
You light your candle for 30 minutes before you go to bed. Then you blow it out.
What you're doing wrong:
If you burn a candle for too little time, especially the first time, you will get that annoying tunneling effect when you have accumulate this leftover wax on the sides of the container (read: you end up wasting your candle).
Solution: Particularly for their first burn, candles are supposed to burn for at least one hour per inch of container diameter. So, if you bought a new candle that is 3 inches in diameter, you should burn your candle for at least 3 hours (though not more than 4 at a time). Wax has a memory, so you want to burn your candle so the melted wax spreads all the way out to the edge of your container. That way, when you burn your candle the next time, it will remember to melt all the way out to the sides.
*Note: Sometimes, especially with cheap candles, the wrong wick is used in the candle, you may not be able to burn the candle until it creates a full melt pool even if you do burn it long enough. This is the fault of the candlemaker for not testing the correct wick, not you. If your wick eventually drowns in wax, you can carve out the wax above the wick and pour some of the wax into the trash so the flame can create a bigger melt pool.
3. You don't trim your wicks.
What you're doing wrong:
Do your candles have a big black ring around the sides of the candles, and do they smoke when you light them? If this is the case, you probably have been lighting your candles for way too long and not trimming the wick. What happens when you light a candle for too long is you've let your wick "mushroom" or develop carbon buildup. This is the result of the candle consuming more wax than it can burn. Lighting a "mushroom" can lead a wick to crackle and pop and release soot into the air and onto your candle container.
Solution: Always trim your wicks to 1/4 inch before lighting, and never burn for more than 4 hours, otherwise carbon will start to accumulate again. Try buying a wick trimmer to do the job right!
4. You blow your candles out to extinguish them.
What you're doing wrong:
This one seems a little crazy huh? How else are you supposed to extinguish a flame? Here's the thing—blowing out candles can cause wax to spray onto your face and smoke to fill the room. Doing so can also bury the wick in the wax making it hard for you to light your candle the next time.
Solution: Use a snuffer.