Just be nice.
Yes, be nice and be kind to everyone you meet.
It is very simple to be nice and sweet to people that you like and who are nice to you. This requires no effort for most of us, and interactions with those people leave us feeling good about ourselves.
The true sign of a happy and spiritually evolved person is the ability to be kind and gentle with people who do not like you and of whom you are not a fan either. Your job in this lifetime is to uplift everyone you meet with your speech, actions and thoughts.
Doing so could be a challenge at times, yet it is a powerful practice that creates miracles. You don’t have to like everyone. And as much as 50 % of people you meet will not like you either. But be nice to everyone no matter what. By doing so you are not engaging into another person’s body of pain (the emotional zoo of animals that live in each one of us, and try to do their best to prevent us from having a happy life) and therefore you are not creating more negative karma for yourself.
Karma is action-reaction. Train yourself to not react and to be forgiving, to be an example of compassion and to see the best in yourself and in everyone. I encourage you to learn breathing techniques that allow you to control your mind, as our mind always follows our breath. When you can control your mind, you will control your emotions and react less, while acting from your highest self. This will always be your tool that you can use during interactions that upset you, to help you keep you own energy for things that really matter, and protect yourself from negative emotions of another person.