For starters, not everyone knows that there is a correct and incorrect way to burn a candle. The first step is to always trim the wick. Trimmed wicks make for a cleaner burn and a far less smoky residue.
Have you ever bought a brand new candle, in a beautiful glass jar only to watch the glass turn black and smoky? There's a way to prevent those ugly smoke stains, and it's incredibly simple: always trim the wick.
Start by trimming the wick to 1/4–1/8 of an inch in length after every burn or every 4 hours.
An example included below:
You can use a plain old pair of scissors to trim your wicks or if you're a habitual candle burner we would suggest a pair of wick trimmers, as pictured. Once the candle burns down, it will get more difficult to reach the blades because they'll have burned down into the jar, so wick trimmers would be best because of its long handle, but between me and you a pair of nail clippers would work as well.