Candles are an amazing way to employ the use of light magic and color magic in your practice. This is why candle magic is a staple across so many different magical traditions.
We don't reuse a candle for something else after we have used it in a spell. So once the spell is completed, we allow the candle to burn down and out by itself.
Never leave a candle burning unattended. If you must leave the vicinity, simply snuff it out and relight it when you return and can be near it as it burns. This will never harm your spell, but it will keep you safer from fires!
Of course, you may always anoint your candles with special occult oils, but you can also use an ancient all purpose anointing oil. It's a simple mixture of vegetable oil (any kind) with a pinch of salt mixed in.
Keep this sacred oil in an air tight bottle and use it to anoint all your candles, or anything you would like to bless (including yourself).