You will really start to build long meaningful relationships
Whether it being with friends or a soul mate you are now developmentally at this age able to start to realize that not everyone stays in your life, but you become more careful of who you are around and how much of your life they take up.
You start to find yourself and who you really are!
In your 20's and sometimes even earlier you start to become aware of who you want to be and what that means. Whether you want to stay in school or become a parent/Spouse it is your destiny run with it but always make choices carefully.
Make decisions wisely but still have fun!
You really do only get one life obviously! We all need to work and strive but aim for a career or a job that suits your individual strengths and talents, if you are not happy change it because in the end there is so little time but again choose wisely with every given decision.
Live for now stop thinking so much about the later
Don't live in the clouds, keep your feet on the ground and roll with each day individually. If you are constantly worrying about the future you may miss what is happening now! This one is still a hard one for me from time to time as a young 21 year old, but I am learning and striving. I quote from the great Ferris Bueller Life Moves pretty quickly if you don't stop and look around once in a while you could miss it.
Try and learn something new every day even if it is small
Try and take on a new goal daily whether it being something big like Learning to drive or something kind of small like learning a new handcraft like sewing, it doesn't matter what you do just keep those brain cells working and fresh!
Stay Busy ...
Don't let each day just be that another day, do stuff go see things, be with people or just what you wan't to do if that pleases you but don't waste time being unhappy, change that.
Try to avoid fights. They're not worth it
Neither are your relationships ending over a stupid ignorant fight. Talk things out and facilitate through a conversation with kind words and peace, because sometimes when you lose a relationship with someone you may never be able to get it back is that something you can live with?
Learn to make decisions more precisely not so quickly!
Stop trying to rush decision making, slow down take your time and really think about it and all you think is what matters overall. Your life your decisions.
Learn from those damn mistakes!
Every mistake should be thought over carefully so that you can avoid making it again, and sometimes making a mistake a second time can be inevitable. This is why we need to stop and think carefully what caused this mistake and what is the solution.
Learn to apologize when you've done wrong and take responsibilities for your actions
If you've done something wrong, simple apologize. Here's a scenario maybe you said something that was unkind, well don't play it off like you're cool apologize dammit otherwise don't feel bad when people do not respect or honor your friendship. Just take the right path and do the right thing.
Be humble and worry about yourself
Ever hear the saying we are as individual as snowflakes when you were a kid? Well that could not be any more true than said here. We all have strengths and Fears and that's what makes us unique, so with that being said don't point out other people's imperfections. Make sure you are close to perfect before judging someone else.
Work your way up in the world
Start slowly and graduate to your goal. We wen't through all these years of school and even if you learned nothing from this experience take away the achievements you did make and realize that they took time and were worth, regret nothing and keep a level head. Things take time and patience and will come when they're ready.
Don't set too high expectations
Now this is not to be confused with not trying out new things, always try new things but have reasonable expectations for yourself so that you do not feel discouraged easily, only do what you can do!