Try this . . . put a smile on your face (even if it feels phony), stand tall and go do whatever your day requires. Whether it is a meeting, or errands, jury duty or just your everyday job. You will find that if you smile, look people in the eye and say hello, or thank you, or please - whichever is appropriate, most people will respond positively to you. Go out on a limb and hold a door open for someone - it works! Even if your errand is potentially unpleasant (like expressing your discontent with with a co-worker's behavior, for instance), if you do it with a smile and acknowledge that the other person is a human being, you will find life generally easier and more satisfying. As JFK said, "A rising tide lifts all boats".
I have tried this experiment many times. It works! And you should always assume ahead of time that you will be received in a positive fashion.
Because facial expressions generally mirror emotion, they are mostly involuntary. This can be altered even if you are not feeling happy - smile and you'll start to believe it!
Let a smile be your companion for a day, and see the difference. Here's a little silliness to help you smile: Jim Gaffigan loves Hot Pockets!