I've had black wheels on my Golf for the last 3 years.
I generally always snowfoam my car when cleaning, so I let the gunk run off for 10 minutes.
I then rinse with a power hose, and apply some Bilberry wheel cleaner - and leave that to soak for 5-10 mins.
I have a Meguiars wheel brush that I use to clean the face of the wheel, and then a EZ Detail Brush that I use to clean inside the wheels - and a mini version for between the spokes. The EZ Detail brush is far more expensive than most, but you can feel the quality.
Afterwards, I rinse, then dry with a microfibre cloth... before applying some Poorboys wheel sealant.
3 years later, and I still have no scratches! Everyone likes their own methods and brands - so I'm not by any means saying mine is correct!!