Picking the right spell candles can have an impact on how successful your candles spells end up, so start off with the right materials next time.
Some spells will specify what color of candle to use, so this isn't always going to be something you need to figure out for your spell candles. If it doesn't say, try to choose the most appropriate color for your purpose, such as:
Love - red, pink or white
Money - green or gold
Protection - black
Health - blue or white
The color provides its own unique type of energy that will help your spell.
Read through the spell before you choose your candles. If the spell is designed where you need to let the entire candle burn out, you don't want to start off with some huge pillar that will last 3 weeks. Well, such a huge candle will certainly give your spell some staying power, it can be awkward and even dangerous to have a candle burning for so long.
In most cases, a small votive candle works best if you are going to let it burn down. A small "chime candle" will burn out completely in an hour or two, which might be even better.
Ok, that covers the spell candle basics, but you can do a little more if you want. If you can get candles that are scented, they can be great as long as the scent matches your purpose. A pine-scented green candle would be better for an abundance spell than a green candle that spells like chocolate chip cookies. Most witches prefer to stick with unscented candles.
You can use oils to anoint your candles (which just means that you rub the oil on the candle before you burn it), and you can also use something sharp to carve signs, words or symbols into your candles for a little added effect.