trim the wick
Candles will come perfectly trimmed for your first burn. For each burn thereafter, make sure the wick is trimmed to 1/4" before burning.
don't extinguish too early
For your candle's first burn, make sure it stays lit long enough for an even wax pool to reach all edges of the jar (approx 2-4 hours.) This helps to prevent wax "tunneling."
Never leave a burning candle unattended. 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. Never burn for longer than 4 hours at a time.