Your first burn is the most important as it dictates how your candle will melt. To prevent tunnelling, allow your candle to burn for at least 2 hours but for no more than 4 hours. Always cut your wick to about 4 mm before relighting, and it often helps if you re-centre the wick after you have blown your candle out.
Your wick may release a small amount of smoke when you first light it. You can either wait for the wick to burn until it soaks up the wax or blow it out, cut it and relight immediately.
I would not advise putting the candle on glass and you should never leave a candle unattended. Always keep it out of reach of little hands!
Please remember that these candles are hand-made and, whilst I try very hard to get an even surface, there may be the occasional air bubble. I can assure you that this does not affect the throw of the candle in any way.