Step
1:
Jack up the car and take off the wheels, if you only
have 2 jack stands just do one side at a time, either
the front or the back.
Step 2:
Clean the calipers. Spray on the brake cleaner that
should help get off alot of the gunk on the caliper.
Just scrub it down some, it doesn't have to be spotless
but clean it off as much as you can.
Step
3:
Mask of the rest of the brake system. Some people
take the whole caliper off to paint them. I don't
think thats necessary. Just tape some plastic around
the rotor and everything else you don't want painted
and you should be good. Here's a shot of my rear brakes
masked.