How do you become your own best friend?
This is a bad idea. While you should have self-respect and a healthy view of your potential/ability, as your own best friend you are talking into an echo chamber that will only confirm and grow your biases.
You want a critical outside party to give you a good smack upside the head when you need it, a hug when you need it, a shoulder to cry on, and even a pity party from time to time, followed with a smack upside the head. You can try to be this for yourself, but it's too easy to uncritically fall into bad patterns.
What's more, you live in the world. You must learn to navigate that world. Instead of looking inside, you might want to engage in a much more fun question: “What can I do today to be the World's Best Friend?” or “What can I do to be X's Best Friend today?” where X is any person you want to connect with today.
There are two things I want to add here. The first is the best way to have friends is to be a friend. A friend does without any expectation of return or profit. He does because he has a commitment and it makes him feel good.
Second, it's not for you to judge if you are a good enough friend. If a person says you are, you are. That doesn't oblige you to anything, other than the baseline honesty and straightness that should be there anyway.
Take it on. If you want you can make it your theme for 2018. And if you are so inclined, come on back here and let me know how it went.