A smile will let people know that you are pleasant. If you smile at someone, look them in the eye. For the most part, if you smile at someone, they won't do anything but smile back. If they don't, then maybe they are just having a bad day. It is up to you to set the mood of the encounter. Make it happy by being the first to smile. Normally, making faces or moody looks at someone is not nice.
While walking past someone, even a stranger, we can try to acknowledge their presence with simple "hello" or "hi" or even just a wave or a nod in their direction. Adding the smile to this can make it all the more friendly. Other parents always like kids that say hello and how do you do, and so do friends.
We can ask people how they are doing. Take the time to ask someone how things are going in their lives, without being nosy or intrusive. If they seem resistant to talking, let it go and leave them alone unless you really know them and feel you can ask. They will then understand that you're trying to care for them and not assume that you are a prying person, which you are not.
Source is Internet.