How do I stop seeking approval?

I used to have the same problem as you, fearing that people may judge me behind their backs, hate me etc. But, I have come to terms that everyone will judge you, be it good judgement or bad judgement. You just have to accept that you can't change how people think, so just let it be and not care about it. It may seem hard at first, but slowly, you'll realize that not caring may be a good thing.

perhaps if you realised that most people are not interested in you.... most are only interested in themselves....

But you should seek someone approval! One person, only though. Yourself. If you approve how you look, sound and what you do (and considering nothing of the previous are illegal XD) then it's all good. You fear people ill-judging you? This is normal, and happens. Menkind and society DEMAND us to judge others, by how they look or what they do. And be glad for it! You won't want friends that like you because they "approve you", or because you dress and sound similarly. Good friends (and relationships) only happen when you are honest with yourself and others, not when you try to please others. Find yourself first, then be it. You'll find inner peace is better than not having strangers giving you the "bad eye". Trust my advice.

Approval is a basic human need, both your own and others'. It becomes unhealthy when you care too much about what others think. I would recommend making a list of People Whose Opinions Matter, obviously with your name at the very top. These should be people you respect and who care deeply about you doing the right thing. Seeking these peoples' approval is healthy, and when you catch yourself acting "people-pleasy" in everyday life you can check yourself against that list and say "I have the validation I need. I'm doing the right thing."