How do you not care about impressing others at all?

I feel like it's a distraction and causes me to lose focus, so I don't get the things I want to do accomplished. All the advice I hear and read about simply say to tell yourself that what other people think isn't important, but they don't give any specific techniques about how to put it into practice and not just repeating a bunch of statements to yourself. I can repeat statements and know something may be true from a rational standpoint, but it still won't change the way I actually feel because the unwanted thoughts and feelings just keep popping into my head automatically.