Wick trimmers are perfect for cutting cotton or wood wicks.
Wick trimmers help maintain proper wick height. You want to make sure to keep you wick trimmed between burns. This gets rid of ash that can snuff the flame and also prevent sooting or smoke from a large flame. Trimming your wick also helps with burn quality and smell.
Prior to each burn simply use your wick trimmer to remove some of the ash residue on the wick but cutting off ash that is easily cut through. Wood wicks typically burn better when trimmed but not so low that the wick is even with the wax.