like kingkaan does, I also have a can of compressed air that I use every few weeks to get the dust out and prevent it from building into a mass that gets stuck behind the heatsink. Just make sure you use short bursts and
do not overspin the fans with the air jet, since making them go faster than they are designed for might damage the bearings and make them noisy.
ASUS G750JX -- i7-4700 - 16GB - 128GB 840 PRO SSD + 1TB HDD - Nvidia GTX 770M - 120Hz 3D glossy display