I'm a little bit late with this since International Women's Day was yesterday and the YouTube campaign has stopped and everything but I have decided to take part anyway because it seems like such a great concept to me and it not only helps yourself but also helps many other people too. :)

Dear Me,
I have never been the best at giving advice but I think if I was going to advise anyone I think the best person would be to advise myself. So that's what I'm going to do.
The first thing I'd like to say to my younger self is that it's okay to want to spend time on your own. You might think it's weird when you get days when you don't want to talk to anyone and just want to shut yourself away and be invisible and that is okay. You are just not a people person. It's not anything to feel bad about and it is okay to turn down plans if you aren't feeling up to them. Your friends will understand, it's just that sometimes you just need to take the day to yourself and just be.
On the other side of that it is also okay to want to be heard. If you have an opinion don't be afraid to speak up and share it. Even if you are worried about people getting offended you have a right to say how you feel. Almost 99% of the time you say something someone is going to disagree but you just have to stand your ground and stay true to what you believe in. It is also important to be careful with the way you word things, while it's important to be heard it is also important to be mindful of other people. Don't go out of your way to purposely hurt someone with your words. Respect that they have a different opinion from yours.
Also stay away from the internet when you are angry. It is okay to rant when you are angry, it is okay to have negative thoughts from time to time but try not to share them with the world. I know I've always found comfort in sharing my thoughts online but if they are hurtful and rude I would keep them to myself. Spreading hatred online can only lead to trouble and you have no idea how the person you are aiming these things toward feels on the other side. 
It is also best not to indirect post about other people. You might be angry with someone about something and you think the best way to let them know you're angry is to talk about them indirectly. That's the opposite of what you should do. I know I've never liked confrontation but it is better to talk directly to the person you have an issue with rather than tell everyone else but that person. Having open communication with people can make relationships a lot easier and save a ton of drama.
I would also advise my younger self not to worry so much about other people. It is okay to care about your friends and worry about them from time to time but you can't force them to get help or change. So don't worry so much you put their needs before your own because this can have a negative effect on you too. All you can do is be there for your friends and give them advice but it is their choice whether to take the advice you give. The most you can do is do your best to help them but  you can't control what they do with their lives. So while you may not agree with everything they do, you should accept them for who they are and hope they will make the right choices for themselves.
It is also okay to let go of the past and the people in it. I know it's hard to let people out of your life but sometimes it's for the best. You shouldn't be holding onto people in your past if it is stopping you from living in the present. While yes, you have great memories with these people you have to accept that that's what they are, memories. You can always look back and enjoy the time you had with them but at the end of the day if things didn't work out it's okay to move on. It just takes time.
And the last piece of advice I would give to my younger self is be yourself. Don't be discouraged by people around you that don't like who you are. Don't let them influence how you live your life because they aren't the ones living it. Find what you love and do it. It is always best to stand out on your own rather than follow the crowd. Be proud to be different and embrace it. Because it's your life and you have to live it, no one else. So don't be ashamed of doing what you love, don't be embarrassed if you don't like what everyone else likes. As long as you're happy with your life, that's all that matters.
Love, Courtney x

And so there's my letter to my younger self. I am sure I would have so many more things to add but I think this covers a lot of it.
I hope you guys enjoyed reading this advice I'd give to my younger self and that you can relate to it and it helps you in some way. I'd also love to know if you have any advice you would give to your younger self because I think even when we are older we still forget basic advice like this. Especially when you are still growing up like me...
Thanks so much for reading. :)
~ Courtney x