1. Not getting enough sleep. "But Anna," you ask, "How can I sleep when there are so many mistakes to make?!" Don't worry, you have an entire decade's worth of days and evenings to irrevocably fuck up your life. (Related: 1.5. Not washing the pillowcases often enough. Once a week, or else your skin will suffer.)

2. Being addicted to social media. He liked that picture of your cat on Facebook, and then you retweeted his tweet, and then you trolled all of his friends' Instagram accounts to try to find out if he was dating someone else, and then he posted a news article to your wall that related to this inside joke you guys have, and by the way, it is a beautiful day outside.

3. Washing your hair too much. Yes, too much, especially if it's not stick-straight! By the time I was 24, my hair had the consistency of tree bark. Skip a few shampoos and just condition, or use dry shampoo! I use Rene Furturer, that stuff in the dark green spray bottle.

4. Wasting money on restaurant meals. I spent the first five years of my 20s dragging my hungover ass out of bed and feeding a $14 artisanal omelet to my mouth. If only I had skipped maybe one of these a week, I'd have $60 extra for grocery money, or for one giant artisanal omelet that we could all share.

5. Being health-bipolar. During the day, we're drinking green juice and going to yoga. At night, we're out partying with friends and ending the night with 4 a.m. fast food. The former does not detract from the latter — your body is just confused as shit. :(

6. Trying to tan. Ack! Stop. Even outside of a tanning bed, UV rays are no good.

7. Spending all your time in a relationship. Friends of mine who were with the same guy all through their 20s are lamenting it now. Before you settle down, you gotta get some strange. To truly appreciate the good men, you have to road-test the bad ones.

8. Or chasing after someone who is completely disinterested in you. Does he never ask you questions about yourself? Swoon. Does he take at least 24 hours to text you back? Nice. Are you in his phone as "Mike" so the other girls he's hooking up with don't know? Yayyy! (No.)

9. Getting sloppy with birth control. It is a joke to try to pretend that it doesn't feel better without a condom, but everyone's gotta. You gottttttta.

10. Getting a long-term pet with a significant other. So you and your boyfriend decided to drop a few of your start-up paychecks on Chuckles the $1,200 cockapoo. If you don't last as a couple, Chuckles is a child of divorce, which we all know is a gateway to drugs and juvenile delinquency.

11. Drunk texting/dialing. And rolling over in the morning dreading to look at your phone. Hoooo boy, do I know what that's like.

12. Going on extreme diets. No matter how many lemon juice, cayenne pepper, and holy water holistic cleanses you go on, you'll end up at your normal weight ultimately.

13. Buying tons of $15 H&M trend pieces instead of saving for something expensive and timeless. A cheapo peplum top (last year) or pleather leggings (2007)ish are always bound to go out of style, like, tomorrow.

14. Splurging on beauty products you know in your heart you won't use. Sephora is in business because "if I just buy this $75 unicorn-horn face powder, everything in my life will immediately improve and I will know what the fuck I am doing" seems logical to you, briefly. It's not true!!

15. Spending a lot of energy on envying someone you have decided is your nemesis. She is the 2.0 version of you, in possession of the career, boyfriend, wardrobe and apartment of your dreams. Or she is just an acquaintance whose superiority complex and complete lack of self-awareness annoyed the shit out of you. (Not that I'm writing this from experience or anything.) Take a breath and let it go.

16. Letting harsh judgments of your friends' boyfriends' (or your friends' harsh judgments of your boyfriend) tear apart close friendships. He's a tool. Just let everyone figure it out on their own time.

17. Letting your office treat you like an intern when you haven't interned in years. Yes, your mom's overenthusiastic friends are right when they tell you "how lucky you are to have a job in this economy." But being a full-fledged employee with a salary who is regularly told to get coffee for supervisors and carry heavy boxes is bullshit.

18. Hooking up (the "feelings" way, not just the "casual" way) with a friend's sibling. If the sibling lives in the same town that you both do, this is the most awkward social decision you can possibly make, besides going to Jay Z's 40/40 Club in a chicken suit or something.

19. Picking the wrong-ass roommates. Sure, she was a good nightlife friend in college. But do you want her walking through your room of the railroad apartment at 3 a.m. dragging some douchey party promoter for a one-night stand? #nope

20. Slowing down. Adulthood doesn't happen overnight. Enjoy the decade — appreciate your wide-open future and perky boobs while you still can.

Follow Anna on Twitter.

Headshot of Anna Breslaw
Anna Breslaw
Writer. Things I appreciate: Ghosts, white wine, men who look like they could protect me from predators, and a great homemade deviled egg. Also, I have a VERY ambivalent obsession with Sex and The City but I'm not like any of them, other than maybe Miranda's cat.