I'll echo the core strengthening routines as the most important... a strong back is a much less likely to be hurt back.
I've always been a fan of the squat exercises, especially for this line of work. We emphasize using our legs for everything, why not start there?
A simple way to get into the routine is this: wake up, do twenty push ups and twenty sit ups. Easy? Do more. Hard? Do what you can until you fail. Then go for a jog of about twenty minutes, either outside, on a track, or on a treadmill.
My mom (45, shhhh!) actually just lost damn near twenty pounds just by walking for a few miles a day on a treadmill. Her cholesterol (always a concern in this line of work, with the crappy diets we seem to have) has dropped like a spent rockets, her endurance and energy are up all day long, and she sleeps better. Did I mention she has a bone spur in her back?
Likewise, my grandfather (73) started volunteering at a conservation center in Erie, PA. He didn't like waiting for the horribly slow elevator everyday to ride up to the 4th floor, so he took the stairs. Six months later, his calves are larger and more muscular than mine (and I'm military!), and he's in the best shape of his life.
Simple activities can be a work out... take the stairs more often, do your morning calisthenics, walk to the store when weather permit... it's all about bring active.
As always, "consult a physician before starting any new exercise routine".
It's hard to tell what to suggest you start with, as far as routine goes, without knowing you any. Are you active, not so much? Younger, older? Male, female? I'm not around here very often, so if that's common knowledge, my apologies.
Try this as a benchmark: how many push-ups and sit-ups can you do without breaking form? Stopping to rest for no longer than 3 seconds.