I feel like my sister is better than me and everything is a competition, what should i do?

[Milly]

That happens to me too. I just have to focus on how I'm better than her, rather than in which ways she's better than me. Try to find some sport or something that you can use to get your mind off of that. When I ice skate, I feel so free, and don't care for criticism. You also may get better at it, and find your calling.
If you need to, talk about it with someone you trust: BFF, counselor, adult, parent, teacher, friend, etc.
Timing is also important. If your annoyed with her, just wait for the right moment. (Spontaneous combustion. JK! Don't really attack her.) If she gets in trouble for something, make sure you have been extra during that time. Or even save something for a time like that, like a good test score or something. It will really get your parents to be like: "see, look how well (your name) did on her (whatever it was). You shouldn't have (whatever she's in trouble for). I'm grounding you for two weeks.