1. Watching back-to-back episodes of The O.C. fixes everything.
2. Especially if you watch "The Heights" then "The Mallpisode" in that order.
3. And it's best if you fast-forward the boring parts about the parents and focus on all the bits where all the right teenagers date each other.
4. Telling other people's secrets to your sister doesn't count.
5. But telling your sister's secrets to other people does.
6. Especially to your parents.
7. Proof-reading homework, personal statements, uni coursework, and job applications is very boring but 100% your main duty as a big sister.
8. Your little sister's main duty is to make sure you don't erase a single cringe teenage phase from your history.
9. The main way she'll achieve that is by telling embarrassing tales every time you try to impress people you think are cool but are actually zzzzz.
10. The first time your little sister goes somewhere a tiny bit dangerous on her own is kinda scary and gives you a little insight into what being a worried mum feels like.
11. And the first time your sister fancies a boy is also even scarier because boys are mean.
12. The best trio of films to watch after a miserable day are The Parent Trap, then It Takes Two, and then The Parent Trap again.
13. Sharing a bed is really boring when you're kids but kinda fun when you're grownups.
14. Same goes for dressing the same.
15. Saying "Sorry if I upset you" is not the same as saying "Sorry that I did a bad thing."
16. Only the second one counts.
17. But you should only say it if you actually mean it.
18. There are two kinds of people: The ones who worry about whether they should go for a hug or a handshake and end up doing an awkward half hug-half pat on the shoulder, and the ones who always go in for a massive cuddle.
19. Guess which kind you should be friends with.
20. Cooking cakes before eating them is overrated.
21. Living in different timezones will make staying in touch constantly really difficult.
22. If anyone is even 1% mean to your sister, you'll feel angrier than you ever knew you were capable of being.
23. And even if your sister forgives the meanie, you'll never forget.
24. The best way to pass time on a long flight is to close your eyes and point at the map in your inflight magazine to work out where you're going to live as a grownup.
25. And also which country your future spouse will be from.
26. And also which country your job will be in.
27. Even if you probably won't end up living in Montreal, dating someone from Colombo, and commuting to Cape Town every day.
28. If your sister ever achieves anything even slightly impressive, you'll feel over-the-top proud.
29. Even if it's just passing her driving theory test, which is very hard to fail.
30. Moving away from each other is really sad.
31. But planning the day when you'll live in houses that attach via a secret attic is really fun.
32. Spending birthdays apart is bad enough.
33. But spending Christmases apart is heartbreaking.
34. Talking of Christmas, squeezing your presents under the tree in the middle of the night is perfectly acceptable.
35. So is peeling back one tiny little bit of Sellotape so you can see like the corner of a gift.
36. BUT THAT'S IT. Any more is cheating.
37. People who make you cry aren't worth hanging out with.
38. Having a sister is really helpful for when you only have a half-memory of something that happened ages ago, because she probably has the other half.
39. And she'll be able to offer perspective on your family when you get too full of rage to see clearly.
40. Even when it feels like everything is bad, it won't be long before you get over it and move on.
41. Rehearsing awkward conversations you don't want to have is much more fun if one of you puts on the other person's voice.
42. Internet people aren't real.
43. If you take a selfie that's so ugly that no one can see it but someone must see it, your sister is that person.
44. Sometimes you have to ignore what everyone else says and just go for what you want to do.
45. Sisters never judge.
46. There is still time for you to be the next Mary-Kate and Ashley.
47. Being kind is way better than being cool.
48. And being older definitely doesn't mean you know more.