i do a stiff Hei Hilter style wave - you can't miss it. I get quite a few responses, and usually do it before they are parallel to me, to give them an opportunity. I know that as I get more comfortable with the road this is easier. There was a period where I was so riveted with trying to keep alive and pedal, that I rarely noticed them until they were passing behind me.

I try to always call out when I pass someone on the same surface. However, I don't when they are on the sidewalk and I am on the street. I've had too many people spook when I call passing on left and even had one dad with a little boy who freaked (dad did), misunderstood me and moved directly to the left - where I was calling I was passing. I've had teenage girls scream bloody murder too When I have to pass peds, I always slow, and if they have a dog/kid, I slow even more.
I try to greet cyclists I pass. I even do it when I'm passing in a group, and I don't know if it has been called. At least a Good Morning can't go wrong. Even if it 110 out and 5pm, we can get a good laugh.

I do tend to ignore folks going the wrong way on the street or in my bike lane, occassionally offering a "you're going the wrong way, sir" in a polite tone (never a gal, I've noticed).