You can change completely a person's day completely by just telling them something nice. It's magical; it's beautiful; it's how they just stop doing their stop to look at you and smile. It's the moment where you become a good memory for them, and you will be in their thoughts when they are driving back from work or washing the dishes because you are now an experience, and probably the best experience on their day.
Let's face it: daily life sometimes suck. And it's nice if someone out of the blue makes you smile and feel comfortable with yourself. Keep in mind that when you give a compliment, you should not expect to get something in return. You are not getting a benefit for telling them so, and there is no follow-up, it's just for love of humanity.
It's a basic need: Belongingness and love. With so few words you will be covering this need to someone else, you will release some Oxytocin in someone's else brain.
That's it. Simple. Easy. Say something nice to anyone, to a stranger or a coworker. Something random but accurate and sincere: That's an fantastic Super Marios Bros shirt!; You are the best Uber driver I've taken!; I love the solution you made! A smile will be drawn on their faces, and naturally on yours as well.
It doesn't matter if you know them or not; if you don't, the better. A compliment will be just one way but will change the day of both parts.
Anything works; just try it.
===
Ref.
Maslow's Hierarchy Needs