over 80% of my bike commuting is in broad daylight (only my evening commutes for the 4 months of standard time are in darkness), so i try to make myself visible with color: bright red bike, stark white helmet, and a bright colorful shirt.
in the darkness of winter i wear a hi-viz jacket with lots of reflective striping + reflective striping on my helmet. and of course front and rear lights.
and of course the most important safety measure: caution
that's about it.