PID control of steering left and right

I am a big fat newbie with Simulink control.

Using a PID controller, I want to steer left and right. At the moment, I am able to proportionally steer to the right (i.e reduced right steering corresponds to left steering). But I like to know how to explicitly steer to the left as well as right.

What is the standard method to determining steering direction? My guess #1 is that I need to use the sign of the error signal to know which direction to steer. My guess #2 is to compute the directive of the PID output and use that to determine the direction to steer? I observed that the #2 allows change in direction to be predicted earlier although it has high frequency components which could lead to several direction changes.