I think the fact that my mom never ever got her knives (or scissors) sharpened when I was growing up & I was constantly cutting myself helped me learn that:
Dull is Dangerous.
Sharp is Safer.
I truly believe that most of the rotary blade injuries are due to dull blades. I've yet to nick myself with a rotary blade, but I change my blade with each new project; sometimes even mid-project if I do a lot of cutting or nick my ruler. My old blades go into a container marked "Used" that I repurpose for cutting papers (parchment, butcher block, fusible, pattern).
I'm starting a checklist for myself so I remember to change out the machine needle, change out rotary blades, oil my machine, oil my scissors. And twice a year I send my Ginghers out to be sharpened/retooled and give my cutting mats a bath. There's so many things to remember to do that I'm finding without a checklist to follow, I skip things. I like gran of 6's idea about writing the date on the blade. Of course, that's only a back-up because it really depends how much I'm using the blade -- on a quilt retreat it might last less than a day.