It's all too easy to get yourself into a lot of trouble. Getting yourself out of trouble is a lot tougher though. As a teen myself, I've gotten in a lot of trouble, but with some really basic and simple steps, I've never gotten suspended or grounded.
First and foremost, an ounce of prevention really is worth a pound of cure. If you are able to refrain yourself from getting into mischief, then there's no way you can get in trouble. Use common sense; even if someone triple dog dares you to light all the posters in the hall on fire, this could result in some serious consequences. That may sound silly, but I actually knew someone from a different school that did that. Needless to say, there was no way she could avoid expulsion. In scenarios like that, you need to put your foot down and refuse to do the dare. If you dig yourself into a hole that is too deep, no amount of talking will get you out of trouble.
As a quick side tip, truth or dare in general is a bad idea at school; the majority of dares can (and will) get you in some serious trouble, and the truths will circle around the school quicker than you would imagine. I've been in quite a few truth or dare games during lunch, and I almost always regret it afterwards. Take it from me; try not to initiate truth or dare in any way at school. Afterschool however is a much better time, and if you play off your school grounds, then you're more than likely not going to get into any trouble. Still, as mentioned above, exercise common sense when taking dares.
But let's say you did do something stupid. Everyone does sooner or later. The next step would seem like a no brainer, but so many people don't follow it. Tell the truth. If you're upfront about your mistakes, and if you're honest and sincere, the odds are that you're punishment will be a lot less severe. Some teachers, especially in junior high and elementary, will even reward honesty with a small treat. One time I broke a graduated cylinder in science. I told the teacher, he smiled and thanked me for being honest, and not only did I not have to pay for the cylinder, but I also got a positive referral and a piece of candy.
Don't let others take the punishment for what you did. If you do shift the blame on someone, it will hurt your social life, and you could potentially lose a friend. If you claim your mistakes, and be honest, not only will those in authority respect you, but so will your peers.
While telling the truth won't always get you out of trouble, it does retain your dignity and teachers or parents will respect you for it. However, there are times when you shouldn't fess up; if nobody is going to ever find out that you did something bad, there isn't much reason to tell anyone. This applies more so with small and insignificant things you've done; use your best judgment on when you should be honest or not. Don't brag about vandalizing the whole school bathroom; word spreads so fast, someone will rat you out.
And last, but not least, be respectful. You need to think in terms of whoever is getting you in trouble; if you seem like a polite and dandy kid, odds are they'll secretly not want to suspend or ground you. However, if you give them attitude then they'll be more than happy to deal out a larger punishment. Think about it; if you're annoying and irritating to them, they won't be rooting for you. They might even keep an eye out for you, so when you do cause some trouble they'll be there. I experienced something like this in elementary school. The end result? A trip to the principal's office. However, following the above steps, she went ahead and let me go with just a warning.
If I had to sum all of this up in one sentence it would be this: Use common sense. You know what's going to get you into more trouble than it's worth. Sometimes doing something is worth getting in trouble. You have to use your best judgment; and when time comes to accept the consequences, be honest and respectful. Even if they may seem stern and punishing, more than likely they'll silently be rooting for you if you come off as respectful, polite, and honest. No matter how clichd it may sound, it really does work. Never panic, never lie, and you'll be surprised how much less you'll get in trouble.