The way I learned was that if an attack is pushing, then pull (step backwards) and if an attack is pulling, then push (enter in).
When stepping backwards, it's done with only one foot stepping back and off the line. The idea is to continue the momentum of the strike or push, in order to pull nage beyond his point of balance. Then, reverse the direction smoothly and circularly.
I thought that this was the way of Aikido and I'm supprised to read that so many styles do not step backwards.