Even those cheapo construction worker safety vests work wonders. You can pick them up at Home Depot or other stores for a few bucks.

Also, I agree on the positioning thing. I have one road which is 45 mph, little shoulder, into the sun morning and evening, with hills. As I crest a hill, if I am going slowly, I try to stay a little outside of the white line, steady and straight (seated). It seems to work so far.