blast of compressed air - they aren't expensive to buy.. and run it under your keyboard as well while you are at it - I also use a clean paint brush for that re any sticky keys....
If you have a can of air use that, blow the air the opposite way to the normal airflow the fan creates (they normally suck in through the bottom and blow out the back or side, so sick the can of air in the back or side). You are best off getting a cocktail stick and sticking it in the vent on the bottom where the fan is to stop the fan from spinning when you blow the air through.
You'll probably get a big cloud of dust come out the bottom when you give it a blow.
DTCWF, Yep I've got some of that stuff... somewhere.
I'll switch it off and give it a good blast.
I don't have any sticky keys, though... thank you very much! lol.