Real simple. Install the front bushing so it makes the front side of the arm longer. Install the rear bushing so it makes the rear side of the arm shorter. I get the center line of the bushing hole and ball joint on the same plane when I decide "where" to install the bushings.
Now for my disclaimer.
That's how "I" do it. Someone will be along to tell me I'm wrong and I really don't give a ****.