First of all hoover the roof to get excess muck and fluffy bits off it. (Sometimes once you have hoovered you find it doesn't actually need washed)
Then i use Autoglym hood shampoo which comes with its own sponge which does not leave any bits of fluff behind. Rinse the shampoo off, wait to dry and spray with hood protector to keep it completely waterproof and as a general protective layer, do this on a dry day or if you have a garage as you should allow it to completely dry before getting wet so that there is an even layer of protection.
Seeing as you have already washed it though get your hoover (i use an old dysen) and hoover the fluff up, it will come right off
Don't bother with a wee dust buster though, i find they just don't have enough power.
Hope that helps
