My biggest tip as a candle maker is to always keep the wick trimmed and short, about 1/4 inch above the wax. This way, your candles flame will always stay small and not large enough to flicker and sway, causing smoke or potential to burn the side of the candle glass. Never burn your candle for more than 3 hrs at a time and always be sure to monitor it to make sure it is burning safely and away from any drafts or moving air.
The link below is a great resource for safe candle burning