For street use you should empty as much out of the car as you can, spare tire, tools etc, near empty fuel tank too. Start on some wet level ground in a place where you can do this in peace without the law getting in the way and ruining your day, a highway at night on a deserted road is alright but bring a friend who can watch the rear tires from outside. Turn the valve in all the way to restrict the fluid to the back brakes. Do some hard stops to get the brakes hot and make sure your rear brakes are adjusted properly, slowly make a few quarter turns out on the valve and do a hard stop in between each adjustment to see if the rears are starting to grab. This can take awhile but usually you'll have a feel for how much a quarter turn will get you. The idea here is to get the rears to start doing their share of the braking without ever locking. Once you get them to lock back off on the valve a quarter turn, then test them again and again until you are sure they won't lock under heavy braking on the wet road. This is the best way to set it on a street car. After your done mark the knob or remove it so you don't accidently change this setting. Some valves are extremly sensitive to even a 1/32 of a turn or half a click so once your close make fine adjustments.
“She may not look like much, but she's got it where it counts, kid. I've made a lot of special modifications myself.”
— Han Solo