When I was a kid starting out with this in the late 1970s, my success ratio was 90 to 100% (rarely ever got a no). But I guess being a freckle face kid who rolls up on his Schwinn bike, looks very harmless and innocent. Now that I'm a ugly mean looking adult guy, my success is below half. Doh!
The best way is to "catch them on their front porch" so-to-speak. You know, like if they're out front washing their car, or watering the lawn, or unloading their groceries from their car, etc.... I will sometimes purposefully, if scouting an old block of homes to find a lawn to do, will drive around several blocks looking for someone out in their yard doing yard work or whatever. Because by catching them outside (and wearing a big smile), your odds are much better. You're not "in their private space" so to speak, when you are just on the sidewalk talking to them.