"On your left" is pretty much the standard.
If I'm overtaking riders I think might not be experienced, i.e on cruisers, I'll make a clicking noise by pulling and releasing the inside shift lever of my Campy Ergos. It's a distinctive noise and will make people turn around and look; then I make eye contact.
That or go wide and get past fast.
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“Life is not one damned thing after another. Life is one damned thing over and over.”
Edna St. Vincent Millay