chezybezy: What I do and always have done, is lightly hold the fan so it can not soon with the force of the air from the can. Spinning them that fast will wear and cause problems. So careful pencil or something to hold out in place works wonders. Just be sure your not contacting anything behind etc. Choose your implement carefully to.
Correction: spin* with the force.
Sorry am on a mobile device therefore cant edit comments.
Elvin37: Can I use something like a paintbrush? to clean it compressed air seems expensive I been looking around today they don't go for less than 15 bucks
A paintbursh would probably create some static electricity which you do not want around your electronics. I agree, make sure you keep the blades of the fan from spinning with a pencil when you use the [url=http://www.amazon.com/Innovera-51505-Compressed-Duster-10Oz/dp/B000U08SYK/ref=sr_1_1?ie=UTF8&qid=137169111 8&sr=8-1&keywords=compressed+air]Compressed Air[/url]. Also, spray it away from your laptop first (on a desk or something), if you see a white film then you need to wait a minute or two (usually means you turned the can too far over)
Really cheap in Walmart and sometimes in your office stores (OfficeMax, OfficeDepot, Staples, etc).