Honestly, I don't think I have anything. I couldn't cope with rejection for a very long time. It wasn't until I found someone that I started to be ok. Now I'm on dating apps and getting matches and messages and that helped me a lot. Like yeah, there will be people who reject me, but there are people who are into me too. Now I'm kind of being rejected in a different way, but I'm ok with that.
I know you can't just make people like you. But I honestly think the best way to be ok with rejection is to find some people who like you. Which is unfortunate because if you could you wouldn't be making this post. It's a classic catch 22. You need validation to feel better, but you wouldn't feel bad in the first place if you had validation.