For an optimal burn keep candle wicks trimmed to a minimum 1/4". Cutting the wick too short can cause the flame to drown.
Candle wax has a memory. On your very first burn, burn for at least 2-3 hours to allow a full melt pool across the whole top of your container. This can be helpful to avoid tunneling.
Any candle in a container should not be lit for more than 4 hours at a time and then allowed to cool completely before re-lighting.. Burning a soy candle for longer than the recommended time could cause the glass to become over-heated and crack.
Never leave a candle burning unattended.
Keep out of reach from children and pets.
For less smoke upon extinguishing, extinguish the wick by dipping it in the wax. Use a specialty wick dipper, skewer, spoon or other long item to dip the wick in the wax pool. Be sure to straighten the wick afterwards so it's ready for the next burn.