Using a mirror really does help you avoid certain situations altogether, or at least it can prepare you for what's coming so you can be READY to take evasive action if needed.
Also, wearing really BRIGHT helmets and clothes helps too. I have gotten some screaming neon yellow apparel to wear (jersey, vest, and windbreaker), and I do feel somewhat safer now. It creeps me out to see how invisible my DH often is when he's riding ahead of me on the road. His dark green, silver-grey, and navy colors just blend right in with surrounding buildings and woodland trees, etc. He just disappears! But despite my frequent suggestions, he simply refuses to wear bright colors and so there's not much I can do.