There are plenty of things that you are advised to do in life and plenty that you shouldn't do. But with age comes knowledge and while I'm only 30, I can tell you right now that this list of things that you should give up will benefit ANYONE at ANY AGE.
 Drastically changing your hair color each month. Trust me, the more you dye your hair funky colors the more dry and brittle it gets. It will keep breaking off and eventually you won't be able to style it or grow it long and healthy. LAY OFF THE DYE!
 Drinking soda. I used to drink soda but the moment I stopped, I had less cravings for it and now I don't even think about it. When I'm out to eat I never opt for soda. Quitting your soda habit will drastically help you lose weight and form better habits. Not only that but soda is SUPER bad for your teeth. Have you ever seen what it does to a penny? Drinking soda is comparable to swishing acid around in your mouth. And don't give me that crap about diet soda. Soda is soda!
 Wearing flat flip flops. There is no arch support in flat flip flops. You may think you're fine now but just wait till you're older. Seriously. It's one of the worst things you can do to your body and especially your feet. You need to your feet to get you around as long as you are alive so shouldn't you start being more mindful of the style of sandals you wear?
 Being afraid to lie. There are bad lies and then there are necessary lies. If you group every type of lie as bad... well just think of it this way... If the guy who hid Anne Frank and her family had answered the door and told the Nazi's that YES, there were indeed jews hiding in the house, she would have been a goner. But no, when they asked, he lied and said no. Sometimes lies are necessary for our survival or even just our mental health. Stop punishing yourself.
 Not wearing sunscreen. People don't seem to comprehend that it's not necessarily the sun in general that's bad for your skin, it's sunburn and sun damage. Everytime you burn you put yourself at risk for wrinkles and skin cancer. WEAR FRICKIN SUNSCREEN. I still get a great tan from being in the sun all day even when I reapply sunscreen like a mad woman. If you don't care then that's fine but don't be bitchin' when you're 40 and have leathery ass skin!
 Obsessing over your weight. First of all, I still can't figure out why so many people don't comprehend that muscle weighs more than fat so if you are toning, your weight will not be dropping drastically. Also, weight isn't everything. Try measuring your waist and chest every once in a while and you'll see more exciting results than you probably would on the scale. And quit freaking out when you weigh yourself DAILY and the number changes. Um, hello... you do realize that depending on when you last ate, how much water you drank, if you went to the bathroom or not, etc. the number will almost always differ.
 Saying that something isn't fair. It's life. Life's not fair. So your friends didn't invite you somewhere, or you have to pull more weight at your job. It's okay to feel that it's unfair but when you get all bent out of shape and you let it affect your mood everyday, and eventually the negativity takes over your life all you will do is push those around you away. When you complain about something not being fair, there is nothing your friends can do but agree and try to make you focus on a positive. If you keep focusing on the negative, you're just creating a toxic environment.
 Being moody. Seriously, buck up. Stop getting butthurt at every little thing. So you woke up 20 minutes late and then got stuck in traffic. Hey, you're alive. And you still have the power to take back your day. If you choose to let the things beyond your control affect your day you will always be miserable. You will only be able to focus on the negative. When you are in a negative state of mind, you look for other negative things to feed you. Trust me, you do it when you don't even realize you're doing it. Focus on the positive. And tell yourself that YOU have control of YOUR mood.
 Being judgemental. I see it all the time. I'll be in a conversation with someone and then a person with pink hair and tattoos walks by and the person I'm talking to stops, stares, and says something like "Ew, why would you wanna look like that". STOP! STOP STOP STOP!! Commenting on someone that is skinny, fat, tall, short, tattooed, pierced, bald, ugly, super pretty, etc.... it's just wrong. Stop being judgemental. I am not even phased when someone like that walks past me. To each his own and who am I to judge. Besides, what makes you so perfect that you have the right to trash someone else. Shouldn't we all know by now not to judge a book by it's cover?
 Eating like $hi*. You will thank me someday. Eating healthier is actually not that hard. You need meat and veggies. So buy frozen fish or chicken. Buy frozen veggies. Start a garden and use your own produce. Whatever you do, it's better to eat fresh than to eat sh*tty packaged meals that are packed with preservatives and sodium.
I may not be a master of all these things but I'm working darn hard to, and you should too!