There's this girl I like in school she's nice, attractive and not fake. Thing is I'm on a totally different planet from her and she doesn't even know i exist. She has many friends and gets good grades when I'm completely unattractive and dumb. I know that it's not going to happen and I don't even know her sexual orientation but I can't stop liking her so if it's possible how can I stop feeling things towards her and never think about her again?
Time and distractions are usually the only methods for getting over someone. Though you can always go the "it doesn't hurt to ask" route and let her know about your crush. No matter how unattractive and dumb you may be feeling, I promise you other people disagree and she may very well be one of them! If you're currently living on "different planets" as you say, then you really have nothing to lose by trying. The worst that can happen is she'll say no and, honestly, knowing for sure that you don't have a chance is a great help in getting over a crush as well...
The first thing you need to do is deal with this falsehood you're telling yourself. Why on earth would you think you're unattractive and dumb? Are you dumb because you don't get good grades? Some of the smartest, most successful people in the world didn't get good grades in school. All getting good grades in school proves is that you know how to get good grades - it doesn't say one single thing about how smart or not smart you are. Are you unattractive because you don't look like the latest magazine cover model? Who gets to decide what is attractive and what isn't? The media? Movies? Comments by others? Are you comparing yourself to some completely unrealistic standard, as most young girls do? My guess is that you're plenty smart and plenty attractive. The truth is that good, long lasting relationships aren't based on "smarts" or "attractiveness" - they're based on authenticity, vulnerability, trust, integrity, loyalty, etc. Anything built on the back of attractiveness alone is going to break down sooner rather than later. Maybe she is on another planet - but that's ok. You can come down on your space ship and be something foreign - something unique and one of a kind. That's what attracts people - someone who is authentic, unique, and comfortable in their own skin. If you come down in your spaceship and she isn't interested - fine! Leave that planet behind for good and go find one that's more conducive to life. Just my two cents.