When it comes to getting the best from your candle, there are few tips take on board.
How to prevent tunneling - 
The wick size is tested with the jar size, so tunneling should not happen, if you burn correctly the first time.
What do I mean by burning correctly?
Place your candle on a flat surface (out of reach of children and pets), light the candle. no need to trim the wick, it's at the correct length.
Allow your candle to burn for long enough that the wax melts evenly, if there is some tunneling happening, let it burn for longer so you have the even melt. 
When you are finished burning your candle, don't blow the flame, incase you blow some of the wax, instead smother the flame but putting the lid back on. 
When you come to relight your candle, trim the top black bobbly part off the wick and put in the bin. When you do then relight, your going to continue to ensure a smooth burn because the wick will be at the right length.