I quit saying "on your left" or "right" because invariably - the person or people would turn that way into me or just stop - now I call out well in advance- in what I hope is a friendly voice - "Coming up behind you" and give them time to turn around, look and move out of the way. I have more of a problem when walking dogs and bicyclist does not call out or zips by me startling me and dogs (startled dogs can run into bike or decide to snap)

Also - when on my folder - I like to ding the bell - but again - more people stop or just turn than move out of the way.