You could search for BrianBraves post when he cut his springs....I think he did about 3/4 in back and 1/2 in front...
I think John is about right.. 1/2 coil, or less, in front and back...
Remember it is easier to cut them shorter if you are too high, but a real PITA to make them longer if you are too low......

You may need the adjustable camber arms in back, even for a small cut.... we already have a fair negative camber before any lowering...