Live a life that's interesting enough that you don't have to speak ill of others for entertainment.
Embrace rejection and failure. They're going to happen several times in your life. Each one is a chance to grow stronger and more bold. "I've been through so much already, why would I let another failure get me down? Why would I be afraid to try again?"
Try not to complain too much. Sure, school might be hard, or there might be a long line at the supermarket, but your troubles are nothing compared to those of the vast majority of the world's population. You have clean drinking water. You're probably going to have something to eat tonight, and every night for the rest of your life. You live in a house, you have a car, and your car may even have a house of its own. Life is pretty good. Life is always pretty good.
Realize that there is no need to show off. Everyone has their own intricate, beautifully complex lives and they sincerely don't care about whatever feat you've artificially bloated to seem more impressive. Have enough confidence in yourself that your own approval is all you need. Similarly, don't be intimidated by someone waving their accomplishments in your face. The most boastful tend to have the frailest egos.
Make an effort in your writing. Language is an amazing tool for expressing your individuality. Proofread everything you write, even something as simple as a Facebook comment. Always aim to be more learned and well-spoken. When you hear a word or phrase you're unfamiliar with, look it up immediately, or write it down to look up later.
Communicate through conflict. It can be incredibly difficult, and you have to really care about someone to talk to them in a sticky situation. It's so much easier to just sit idly by and watch a friend continue hurtful behavior, or to lie to someone instead of telling them a difficult truth. But the hurtful behavior will continue, or the lie will unravel. And then relations fall apart. Be brave and be caring; say what needs to be said. To not communicate is to be a coward.
Conversely, if someone is communicating with you, then listen. They're showing you an immense amount of courage and affection. If you're dismissive of their words, then you're showing them that communicating with you is pointless. Relations won't last long after that. It takes courage to speak, and it takes courage to listen. Strive to do both.
Depression and suicidal thoughts are absolutely natural and should not be vilified or ignored. Honestly, I think if you're in your 20s and you haven't thought about suicide, that's abnormal. I don't necessarily mean that in an 'actively wanting to kill yourself' context. Thinking about suicide can just mean imagining how other people's lives would be affected after you're gone. Close friends, peripheral acquaintances, and total strangers would be affected in three completely different ways. Reflecting on such things helps you realize your place in the world and achieve self-awareness. My choir conductor in college explained the concept of self-awareness to me, and how it simply meant, "knowing how you affect the people around you." That's stuck with me ever since he said it, and that small piece of wisdom has given me a constant goal in life: to achieve self-awareness. If you are reading this, sir, thank you.
While I'm ranting, I want to thank anyone and everyone who's talked to me in the past year. Whether it was real talk over beers, or telling me you appreciated my jokes, or just a smile and greeting in passing, I appreciated it. I've been in a bit of a melancholy place and I fear that it makes me unapproachable at times.
It took a while for me to find my center. Things haven't gotten worse, but they haven't quite gotten better either. That's just the nature of life, I think; not just for me, but for everybody. In hindsight, life can seem like a series of ups and downs, but in the present, it can be long, static stretches of "meh." The stagnancy and ennui can be soul-crushing, and I think most people are faced with them all the time. You may be feeling bored, stressed, anxious, and frustrated with life, but so is everyone else. Have some empathy and be kind to each other. Life is about people, after all. Making each other laugh, driving people home at 4am, giving and receiving gifts. You remember those moments more fondly than a number on a piece of paper, be it grades or salary. So be good to each other, always. The universe may not always punish the wicked or reward the good, but if you take care of the people around you, no matter how awful life gets, at least you can hold your head high, with clean conscience and cheerful mind.