Lets start with the basics:
Never leave a candle unattended.
Keep burning candles out of reach of children & pets.
Burn candles on a heat resistant surface.
Trim the wick after every burn to avoid smoking.
Avoid standing your candle in a draft as this may also make it smoke.
This is known as funnelling, which means that you probably haven't let the candle burn long enough initially. I recommend you burn your candle for 2-3 hours when first lighting it.
Yes, I recommend trimming after every burn when the candle has cooled & reset (trim it to 5mm). this helps to avoid smoking.