Think critically and skeptically, but also don't dismiss advice from those older than you off hand. Helping to raise my god daughters has taught me that most of parenting boils down to trying to minimize the number of fuck ups your kids do that you did. Sure you can't keep them from fucking up totally, but you can at least try and keep them from fucking up the same ways that you did. So listen to them when they advise you on things, but still consider the advice. They could be just as full of shit as you think they are, on any given subject.
Take some kind of job that requires you to interact with the public, especially customer service. You develop a better appreciation for people who are serving you when you've been on the other end of that equation.
Always, ALWAYS be nice to the people who have access to your food. Seriously, nothing good can come of you being an asshole to the people who are making/serving your food in public. They have SO many ways to fuck with your food if you piss them off, don't give them a reason to. Be polite to the person in the drive thru, ask them how they're doing today, be sure to say thank you and sound like you fucking mean it. Be VERY nice to them, because many of them are angsty teenagers/young 20's like yourself, and you know how vindictive you can be when someone pisses you off. So don't encourage them.
Learn how to talk to someone about a subject you know nothing about, and actually be interested in it. I'm not saying "fake it", but just remember, that thing that you love, that you totally geek out about, and think is the coolest fucking thing in the world? They've got something like that too, and it might be something that you find totally boring. But to them, it's the absolute coolest fucking thing in the world. So remember that, and ask them about that thing, and why they enjoy it so much. You will endear a lot of people to you if you can make them feel like their interests have value and merit. The easiest way to shut someone down, and make them not want to engage with you, is to make them feel like you don't care what they have to say, or find the things they have interest in stupid/boring. Don't do that. Show interest, ask them about it, give them an opportunity to geek out about it, and let them know you enjoyed the conversation. And honestly, you might find the subject at least interesting to learn about. Doesn't mean you are suddenly going to geek out about it too, but it let's them feel good to know the person they're talking to isn't just humoring them, or clearly doesn't give a shit about what they have to say.
I'm sure there are other nuggets of life wisdom I could list, but I can't remember them right now.