How to be mature:

Step 1: Mature people don't swear like a semi-automatic.
Step 2: Mature people don't do the right thing because they want praise, It's because you don't want to end up in hell.
Step 3: Mature people take criticism as what it's definition stand for. There's a fine line between insult and criticism. Insult means saying something that hurts another's feelings. Criticism is helpful advice that, should you follow, will lead you to the road of fulfillment and prosper.
Step 4: If you see someone smart and hard-working, they are not being the teacher's pet. They're cementing their future.
Step 5: Don't be mean to people based on their behaviours and looks. Not everyone is as perfect as you.
Step 6: Mature people use smileys only as appropriate. Good example: Can I borrow? =] Bad example: I just ate dinner. O_O xD
Step 7: Mature people don't litter.
Step 8: Mature people know that their parent's work hard to put food on the table. So know how to appreciate what you already have and don't whine like a six-year-old.
Step 9: Mature people respect teachers, and whatever they do is good for you. Unless the teacher's a dipsh*t. Be rebellious and you'll look like an asshole.
Step 10: Mature people follows the rules, even though "my friends are doing it".
Step 11: Mature people respect other people's enjoyments. People are given tastes. They use it.
Step 12: When arguing, do not bring religion in. It's unfair.
Step 13: When you get punished, know that you deserved it. Don't say crap like "This teacher stupid." Whose fault is it that you "forgot" to do you homework that was given to you days ago?
Step 14: Mature people type "you're" when they mean "you're". Not "your" as in "your so pretty". It makes you sound redundant.
Step 15: Mature people are not attention whores.
Step 16: Mature people don't act cute and make kitty-poses when taking photos.

(More updates are added when dates and shown besides them)