I have found a rocket blower is good for just shifting dust and if the sensor has been really bad a wet clean has always worked for me using swabs and eclipse fluid form
here. Having said that on one occasion it did take a couple of attempts.
I have read good things about the artic butterfly OldBoy recommended also.
Just take care when cleaning the sensor though but on the same token don't be scared as with a little common sense and care it is straight forward.