if someone is going to rear-end you, there's not much you can do (even if you can see it coming), other than brace yourself
Anecdotally, it depends on how far away you see it coming. I'm constantly scanning front, rear mirrors, and side mirrors and if someone is driving erratically I take steps to get out of their way (in a safe and predictable manner of course!) I have no evidence this keeps me safer, but this and other "traffic calming" behavior I engage in makes my commute less stressful. It has the nice side-effect of continuous practice that reinforces good driving techniques.
.. and by "brace yourself", you would touch your head to your headrest so that your neck has nowhere to move/flex with the impact. You want all of your body to be completely rearward in your seat.
Also, while this may be morally negative, if there is another car in front of you, you could creep forward and lightly touch their car with your own, making yourself the middle ball in the Newtons Cradle[1] that your three cars now describe.