Here are some recommendations from Brooklyn Hearts Candle, on appropriate maintenance and safety for optimal burn duration and pleasure of your candles.
A burning candle, like any other, should never be left unattended.
Keep wicks trimmed to less than 1/4" at all times for optimal burn duration. The longer the burn period, the shorter the flame.
Allow 3-4 hours for the wax to liquefy across the top. Extinguish. Allow the wax to cool completely. Trim the wick to less than 1/4" in length. Relight.
Don't burn all of the wax in the bowl or all the way down to the exposed wood. Simply scrape away any residual residue with a spoon.
Candles should not be burned in a draft. It is dangerous and might cause the candles to burn unevenly.
Candles should be placed on a hard, flat surface or tray that will not be harmed by heat, flame, smoke, or if the glass or bowl breaks and the wax drips or spills.
If a candle splits or breaks due to heat, smokes, or catches fire, do not burn it near furniture, draperies, carpet, paper, or anything else that might catch fire or be harmed.
When the flame burns out, wash the wooden dough bowl with liquid detergent, allow to dry, and your bowl is ready to be repurposed as a catch-all tray, planter, etc...
The wood bowls are pre-treated with a flame retardant, have a thin hard wax covering on the bottom layer, and have extended metal wick tabs to restrict the wicks from burning all the way to the bottom. Do not burn the candle all the way to the bottom, where the wood will be exposed to the flame.
Remember to reduce the wick to 1/4" before trimming and relighting, and don't burn for more than a few hours before trimming and relighting. This will extend the burn period and help avoid smoke and overheating, which can cause the candle to shatter or catch fire.