I have a friend who gave me this advice, but should I follow it?

She told me that I should do whatever I wish, as long as it's not illegal, rather than basing my actions on what other people think. She thinks that I should start judging myself rather constantly seeing how others judge me. I have heard this before, but to me, it sounds just like an ideal; it is not practical. I feel that if I do not act in accordance with others, I will not gain acceptance, which can lead to other inconveniences in life. What should I do?