I have learnt over my few years living this life, that there are a lot of people who will try to knock you down, put you down, to make themselves feel better. Sadly, this will always be the case, and there will always be someone trying to take your place. Fortunately, there is a way around it. Confidence. If you don't believe in yourself, how can you expect anyone else to. The girl who teased you through high school, or the guy who played with your heart, they mean nothing, because they didn't notice the real you.
The only way to become something in this world, is to believe in yourself. Believe that you are beautiful, that you are smart, witty, and people will believe it to, because it all comes down to how we sell ourselves. 90% of what we say is through body language, if you hide your self in the corner or hang your head in the hopes that no one will notice you, well you are taking away your own voice.
Love yourself. Here's a little tip of my own, find three good things to say about yourself every morning, (they don't have to be the same three things), but three things you are proud of, that you love about yourself, and believe them. It can be anything, from the likes of 'I have a ridiculously high IQ', or even just, 'I have pretty eyes'. But believe it, and believe in you, and things will get better.
Song of the moment: Aloe Blacc - I'm beautiful