Take a pinch of a paper towel.
Feed it through the eye of the cleaning rod.
Give the paper towel a little spritz of 100% PURE SILICONE spray. Anything but 100% pure silicone will damage your gun. WD-40 is one of the worst things you can do to your hop-up and bucking.
Run the cleaning rod down your barrel a few times.
Run it in until it stops at the hop-up.
Pull it out to the end of the barrel and repeat this process a few times.
See the debris from inside the barrel? This barrel is pretty clean but you might need to repeat the entire process of your barrel is really dirty. Don't be a n00b, clean your barrel.