Last year I did something similar where I shared lessons I've learned through that year and it was really fun to sit down and reflect in all the things I've lived and the lessons I've taken out of them, some have been fun, some have a lot of pain behind them.
You are only this young once, enjoy it, this one was one of the first ones that hit me, I've only going to be 20 years one time in my life, there's a lot of things I still want to do and I won't be able to do them if I stay in my bed seeing other people do them.
Be spontaneous, when people think they have you figured out, change, but it's always nice to find a balance in your life, that way you can get the best of both worlds and you won't stop pursuing your dreams and you'll have fun and amazing adventures.
Your health is the most important thing, when planning something new or working on a new project we give everything but we forget that if we don't take care of ourselves we won't have the energy to do it, you only get one body, take care of it, work out, it helps you balance your mind when it's feeling overwhelmed. 
Don't be afraid of new things, new opportunities and experiences always seem scary at first, but it isn't until you actually go out and do it, that you understand how fun it was, say yes more, you only get amazing opportunities once.
Learn to say no, not everything is going to be good for you, don't let anyone pressure you into anything, you are capable of making your own decisions, you are the only one that knows what's going on in your life.
Friends come in all shapes and forms, and that's what makes them special, don't look out for people with the same taste as you, it will be boring, look for people that can make you grow and try something that they may like too, you'll be surprised of how many new things you'll be trying just by listening to them.
Don't be afraid of food, eat until you are satisfied, find a balance, eat healthy, but never be afraid of food, don't see food as calories, and if you are going to change something in your body do it for yourself, you are your toughest judge. 
Sometimes it's nice to take time off, when things get too much, go out, let your mind wander free and don't worry because everything has a solution, you just have to let things be, if it's meant to be, it's going to happen, if it doesn't, it wasn't meant to be for you. 
Learn to love and cry when needed, don't cage your emotions, let them take control, the more you try to control them, the colder you are going to become, remember that you are only human, you feel pain and happiness, don't let those moments slip away, being vulnerable is not a bad thing. 
Work on yourself, work on your posture, workout, be the best version of yourself you can be, make yourself proud before making others proud, feel good in your skin, feel confident every time you enter a room and don't let anyone make you less.
The last one is the most important one for me, keep the ones you love the most, close to you, sometimes we let life take over and we forget about even texting them, it takes a second, don't let any people you love out of your life, they are the ones that are going to make you better and brighter, if they love you they are going to support you and help you through bad times and you should do the same for them.
I feel like there's a lot more I could talk about, it's been a good year, but I know I still have a lot more to go, this time unlike any other years, I'm happy to face everything that life has to offer, I want to make the most of this and be more adventurous, thinking outside of the box is something fun that I don't do enough, we'll see how everything looks next year.