Make sure to burn your candle for at least 2-4 hours on the first burn. Make sure that your wick is always trimmed to 1/4’’ before burning.
To be additionally safe, when the wax level is from 1/4" to 1/2" from the bottom of container, you should discontinue use and avoid the possibility of the container cracking.
Glass containers are particularly fragile and heat concentrated in one area could cause the glass to break. Never burn your candle for more than 4 hours at a time.