Don't say things that make you feel weak
This is Peterson's most important piece of advice!
"Don't say anything that makes you feel weak."
It's great wisdom. We can all agree, but agreement does not magically rewrite decades of your brain's programming. If it did, we'd all be hyper-enlightened Musk mega-Jesus'.
So - the advice is to not say anything that makes you feel weak. I agree, now what?
Now you formulate physical practices that you can act out in the world to gradually rewrite your brain's circuitry. This is not some BS I made up, it's well documented in positive psych, CBT, and basically every book on habit formation.
Here's a great thing you can do, and I seriously recommend actually doing it -
Sit down with your friend, look them in the eyes, and take turns saying things. Start with massive lies and massive truths. "I am a human".. "I am president of the US".. And take careful note of how weak or strong you feel after each statement. Make a plan to do this every time you hang out. And stick to it. Eventually you will start to gain an intuitive sense of when something you say makes you feel weak, and when something makes you feel strong.
And if you agree that's a helpful exercise, and you don't do it, then case in point - this site is a necessary augmentation for Peterson's teachings.