You may often see players use chalk or form for wax to get better grip on the darts. A good way to keep the grip on the dart is to make sure that they are clean. A new set of darts the grip is good, but when you have played them for a couple of months or so maybe less, the grip on the dart is not that good anymore, because grease or fat from your fingers affects the grip on the darts.
There is a easy way, find a container that can hold your barrels, add 20 ml of washing up liquid, and then fill the container with warm water, make sure the barrels lie in the container over night. Then simply remove the barrels out of the soap water and rinse them with clean water and wipe them dry.