If you have spent money on alloy wheels, you want to keep them in the best conditions possible. A scratch or unwanted dirt and debris take away the desired cosmetic effect you bought them for in the first place.
A few things to bare in mind when cleaning to do to so is to clear as much of the loose dust and filth off them as much as possible with either a jet wash or a hose. Do so one wheel at a time when cold and try and avoid getting brake dust on your paint work if you decide to clean the wheels first.
Once you have cleaned you alloys apply your wheel cleaning product. Its preferential to use non-acidic based products as they are safe to use on all wheel types. Make sure you follow the instructions strictly as instructions and applications vary from product to product.