Once you touch the mitt, sponge, or wash pad to a dirty wheel, NEVER EVER let it touch the paint again. Brake dust will scratch.
Some on the forum jack up their car and take off their wheels and clean them then. A good wheel and tire cleaner is EF Hi-Intensity. Wet down the cool wheel, spray on a small amount of EF, let sit for 1-2 minutes, then agitate with a foam brush/sponge. Rinse.
This usually gets 99% of the brake dust and dirt on the wheel, even on cars that have not been cleaned in 2 months.
Follow up with a quality sealant and you can use a seperate bucket, seperate wash mitt, and shampoo to wash down the wheels weekly to restore that shine.
Hope this helps,
Jason