Priming a coil is only done if the coil is new, you don’t have to do this every time you refill your device.
Priming a coil can prolong the life of any coil due to the coil being well saturated before use, meaning the wire and cotton that a coil is made up of is properly soaked of e liquid. This can make the coil last longer, limit the amount of dry hits and maximise flavour.
To prime a coil properly you need to put e liquid on the white cotton parts that are visible on the coils body. Then fill your device and leave for ten to fifteen minutes before use.