A friend told me once she cared too much about what others thought about her. The easy thing to say there is, who cares what others think? It's a good mindset. But there is one person you have to keep in mind. You can be yourself, but you also have the option to be the best version of yourself. Imagine seeing yourself from the outside. You know and you've met plenty of awesome people. What about them was awesome? Now be awesome. Be someone you'd want to be with.
Sit up. Walk with your chin up. Speak up. Cheer up. Up's a pretty good guideline for these kinds of things.
You know you have a judgemental eye, even if you try not to. Think about turning that eye on yourself. Suddenly it becomes a lot more useful. Take it off your friends. Your teachers, your co-workers, and especially off strangers on the street. Just save a little bit of it for yourself.
It feels weird. To look at yourself like that. To look at yourself from outside your body. It takes a bit of imagination. And a lot of practice. But try it. You might learn something new. People don't say a lot of things. Just like you don't either (which is mostly a good thing). And if you're feeling gutsy, it might even be a good idea to ask. You might be in for an unexpected surprise (pleasant or not).
Whatever you see, there's always room to grow. To improve. Otherwise, what's the fun in it all? And don't get discouraged if you have a lot of room. It sounds cheesy because you hear it all the time, but we really do learn the most from our failures and mistakes, not from what we're already good at. If we suck it up, we get better. It takes time, and you might not be able to spot progress each day, but it's there. The good stuff doesn't come easy anyway.