I park on the flattest part of my driveway. I have already set my ride height by measuring from the center of the wheel openings to the ground.

I don't worry if the string is perfectly level. I just make sure the two sides of the string are parallel with each other and just touching the front edge of the rear tire. The string also contacts the rear sidewall of the tire and connects to the other rear tire under the back of the car.

Because of interference with the car's body, I have to put the string down a few inches below the hub centerline.

I use a 10 inch long level to set the camber on the front wheels. it fits nicely on the rim bulge that goes around the lug nuts.

You have to do the toe last after you get your camber set.