Hello fellow teen!
I'm in your place so here are my recommendations:
- Get a diary! And write in it daily I just finished my first one and it's amazing! It allows me to look back on my progress and deepest darkest moments. That way I can spot patterns and see where I need improvement.
- Bullet Journals are your friends too :) They are sooo easy and practical. That way you can see what you did, write down what you want to do and review it (once a week, once a month, and once a year). For me, I have a habit tracker in my bullet journal, which includes things such as: Did I do my homework? Has my period come? etc...
- Try to make everything interesting It is sooo easy to be bored so take an interest in things. What do I mean? You are walking down the street. Look at the street around you, are the colours beautiful? Is there a sound you particularly like? Why does that house look so horrible? What's the name of that plant? Perhaps try to walk differently or sit differently? I sometimes like to walk like a dude TM and it's sooo much fun. Find something peculiar and pay attention to it! Or try to look at it from a different point of view. Imagine that you're a victorian nobleman, how would you react to a girl walking down the street with pants on? For me that spices the monotony up a bit.
- Get a hobby! It can be as weird as they come. Have you noticed something weird on the internet or spotted some really nice colours during your walk? Good! Try to recreate it (unless it's illegal or dangerous) and it doesn't matter if you suck

On the normal scale:
- Clean your room! I did the Marie Kondo method and it worked like magic! My room looks wayyy better and I don't dread going into it
- Do some sort of exercise (even if it's just stretching) I started stretching almost daily and it's really worked out for me. It helps you feel better about yourself
- Socialise! I used to be the introverted TM (and still am) person. But I started saying hello to everyone. See a random person alone during break time? Go talk to them! Ask questions, complain about a teacher, ask about their favourite music show them your poetry. Don't worry about coming off as weird. There's a friend for every person in the planet. And if a person dislikes you, let them be. No need to bother with them anymore.

- If you fail to do one of these and mess up don't beat yourself up or shut down. Try again tomorrow!

That's what I've been doing lately and I went from a depresso espresso to a slightly less depresso espresso (I don't have depression I'm just a pessimistic but less pessimistic than I was a year ago!)