It sounds simple but it is key: Keep the wax pool free of wick trimmings, matches and debris at all times.
How to clean candles?
You can remove dust and fingerprints from a candle by gently rubbing the surface with a piece of nylon or a soft cloth. The cloth can be dry or slightly dampened with water
To remove dents and scratches in the wax, gently buff candles with a nylon stocking to restore shine.