What year, make, model, vehicle?
Stock Calipers? Painted ? Factory Painted ? What Color ?
What have you tried or used so far ?
Can you possibly remove the wheels to do this ? It will be so much easier to have full access to the front and back sides, and while you are there, clean out the entire fender liner and spray a nice conditioner on it to turn it all nice and black again..
In the case where Steam is not available, a good wheel cleaner will usually get the calipers cleaned up of the majority of brake dust, etc...
You will need to get the right brush to help get in between the wheel and caliper and scrub it to remove the more embedded gunk...
Here is a brush that might work if there is room -
http://www.autopia-carcare.com/daytona-wheel-brush.html#.U9qQFPldWSo
If you use a brush like this - you need to be careful on the backward stroke if you are doing this with the wheel on, that the design and bristle length of this type of brush will want to spray straight back, so do not stand, sit, or kneel, directly behind your work, or your white T Shirt will have black spots all over it that wont always come out..
Good luck !
Dan F