I just make sure to wipe everything down good with a damp cloth. I then go back over the black stuff with Mcguiars NXT Trim Detailer, gives it a rich black look, but its not greasy nor does it attract dust like Armorall. If you do this often, it shouldn't get that bad.

Depending on how bad it is, you may need to hose it down like the guys above mentioned.

Heres a pic of mine currently

 

after you get a good wash just wipe it down with a wet towel every time you change the oil. the hoods already up and it only takes about 2 minutes

 

That would work well, doesn't have to be detailed, just cleaned.

 

I leave mine dirty...GM's need dirt to hold them together J/K...