Wandering around pinterest and this post about "Tricky People are the New Strangers" popped out at me. So I followed the bunny trail and read the article. It is pretty good, you should read it. The comments following will drive you batty though, so I will warn you about that.
Basically it is an article explaining to parents why teaching your child "not to talk to strangers" just doesn't work. I completely agree. We never have given that advise to AJ as he needs to talk to strangers all the time and often it is us as parents encouraging him to do so.
As he is getting older he needs to gain the confidence to speak up when needed. We encourage him to ask questions, be assertive - that means speaking to strangers often. We have stopped ordering for him in restaurants, he is the one who needs to ask if he can make substitutions or ask for a refill. When travelling last summer we went through a drive-thru and our order was wrong. I gave him the receipt and sent him back in to get it fixed. It's a little scary for him at times, but he gets better each time and is proud of himself afterwards.
We also use times when we are out to teach manners. Not just please and thank you, but things like looking people in the eye, speaking up and not mumbling, asking others questions about themselves and really listening, holding the door and looking for ways to help someone else. The Boy Scouts call it "do a good turn daily".
These things don't just occur naturally for everyone, some need more practice than others for it to feel natural. So, look for opportunities everywhere and let your child feel a little uncomfortable every now and then. It's the stretching of their wings before they fly!