Paper and pen
Black candle
Cauldron or heatproof dish

Take a piece of paper and write the words:  
 

"I break the bad habit of ___________" 

Over and over again until it fills up the page. If you wish, you may use the back of the paper too. Keep going until you feel it beginning to purge from your system.

When you have finished, light a black candle, chanting: 

 
"Black absorbs, Black Banishes, 
As it burns, my habit vanishes" 

Think of the habit you wish to banish as you chant.

Take the piece of paper and carefully set it alight using the candle flame. Drop it into a  cauldron/heatproof dish and let it burn completely away. 

If it doesn't burn away in one go, extinguish the candle and repeat the spell the following day, and keep repeating the spell until it or the candle has burned away.  

Dispose of the candle stub and any ash from the papers in a flowing stream. If you feel your habit returning, you may need to repeat the spell.