When you choose to see the good in others, you end up finding the good in yourself
The best way for you to learn to always see the best in others, is to simply practice it.
Every day, start of by picking a person and write down all the good things about them. You can start of easy, by picking somebody you love. For each day that passes, make it more difficult by picking people you are less fond of. When you have been doing it for a while, pick people you really don’t like.
During each day, whenever you interact with people, think about their good sides, and about the good in their interactions with you. If it’s hard, think about what good intentions they might have. Believe it or not, but all people have good intentions, regardless of how difficult it is to see.
Continue practicing these to habits, and you will eventually see the good in everybody. And you will be a better person.