Prime ‘raw’ wick by dipping it in melted wax a few times to stiffen it. This helps the wick to burn better and prevents bubbles releasing from the wick into the wax of the candle. Wick should be chosen to suit the diameter of the candle and if you’re not too sure it’s advisable to go down a size, apart from when using beeswax as it is more viscous than paraffin wax so you would need to go a size up!
As an example, for a candle with a diameter of 76mm, it would be advisable to use a wick. Wick sustainers are used to secure the wick in glass containers, or for hand moulded candles.