I knew someone once who was just a plain negative person. She never seemed to have anything nice to say about anything; on the contrary, she had a running commentary going about everyone and anyone. I challenged her one day to point out three nice things about each person she said something negative about. She did it because she loved challenges, but what it did was change her outlook not only on the people around her but also on herself.
People like to be liked. If we go around pointing out the negative things in people, whether verbally or in our heads, we are sending the message out that what we see is negative. And that message goes back to us too. It is only when we are feeling negative about ourselves in some way, when we don't like ourselves, that we become negative about others, and by being negative, we reinforce the feeling of not being likeable. It makes much more sense to do something positive when we're feeling bad, because doing positive things makes us feel good.
It feels good to compliment people. It lifts us out of negativity. If you're feeling down about yourself, give it a whirl. You don't necessarily have to compliment them verbally, you can do it in your head. But complimenting people verbally gives them a gift as well. It can be as little as "I like your bag." People don't care. They like to be told nice things.
Today, I challenge you to notice when you're having a negative thought about someone and then to contrast that thought with three positive ones. Why three? Because one is easy. Two is a bit harder. Three makes you really focus on it, and it makes you realize that you can find the positive even when it feels like it's hard.
There's always something beautiful around you. There's beauty in you. Noticing it in others brings it home to you.