I like to announce my presence with a couple of dings on the bell. It's kind of a gentle, friendly sound compared to a horn or a yell, and it immediately says "bike." Then I'll say Hi, or Good Morning, or whatever, followed by "I'm passing on your left" and a Thank You as I pass. This works in our area, where the MUPs are plentiful and uncrowded. In heavy traffic, it might get wearisome, I guess.
Pets, kids and headphone wearers are a different matter. You just have to go slow, be patient, and be ready to stop.