The difference between Losers and Cool Kids is Reputation.
If people aren't talking about you [your tumblr], you're probably not interesting.
All you've got to do is give yourself a Bad Reputation and you'll be the center of gossip in no time.
People who do drugs are interesting, but they're also usually failures.
The trick is to seem like you do them them without actually having to (and risking premature ageing).
Wipe your nose anytime you exit a restroom, develop a nervous twitch, leave the room anytime you make phone calls and be generally untrustworthy.
Choose one that suits you:
Bipolar Disorder, Anorexia, Depression, Anxiety, etc
Read [watch] "Girl, Interrupted" or "One Flew Over the Cuckoos Nest" for reference.
Studying and reading should be done in private; you should only ever be seen at night, on dates with suspicious men and/or partying with the Wrong Crowd.
The idea is to look like you haven't slept in days and spend too much money on taxis to afford new clothes. Everything should be ripped or wrinkled and makeup should be haggard (one blue eyelid, one green, etc).
Follow these tips and you'll be an "it" girl by April.