Stay happy always.
No matter what life presents to you, always have a feeling of pleasure and enjoyment about it.
Do not ever compare yourself to others. The reason why most people are unhappy is simply because they are looking at what others have that they do not have. They do not feel beautiful because they don't look like what society defines beauty as, but really you are beautiful and as good as the next person is. In fact you are different and unique.
You might not be good enough, your values may not be perceived, some may take advantage of your flaws and weakness(es) and cause you pains. But listen, nobody has the right to ride on your happiness!!! Keep pushing, delete those painful memories from your brain cells. Never allow them get to your self-esteem, rather work with every criticism and get better. Focus on your dreams and let your results speak for you.