"On your left" only works for those understanding what the term means. Same with "Hit the deck", etc. If you have no familiarity with such terms you will likely look around trying to figure out what the hell is going on.
I'd suggest a small bell on your handlebars. The "dinging" sound carries far and is a more widely understood notice of someone approaching. Whether they get out of your way or not is another thing...hehehe.

I generally give a whistle when approaching someone. I'm far enough away to be heard clearly. I pass with more room between us than normal to create a safe buffer...but I ride on nearly empty, rural roads and it is easy to give a wide buffer zone if necessary. I always slow down for a few seconds to say "hi", "great day for a ride", etc. then I'm on my way.