The advice I was given when I was your age was to focus equally on nine different aspects of life, and every day or at very least every week, do one thing to enhance each aspect of life. Treat them all as equally valuable even if they don't feel like they are. Yours could be: healthy living - eating well and going for walks, your relationship with your boyfriend, your home environment - that's three. The 'rule' I was given is that one of the nine has to be giving back to the community in some way - so working for a charity or community scheme. Maybe you could help at Frank or a similar anti-drugs charity or a charity against modern slavery as a lot of cannabis grown in UK uses slaves to grow it.
Give yourself small goals. Better to start small and build up. So go for a 10 minute walk rather than no walk at all, and increase the time of the walk by 5 minutes a day until you are going on a longer walk.
Same with your home - tidy up for 5 mins then stop. Next day tidy up for 6 mins then stop. Gradually you build up a tolerance for more focus. Always reward yourself even for achieving a tiny goal, even if it's just by patting yourself on the back or doing an air punch.
Create some really fun bucket lists - they don't all have to be massive or expensive - just enjoyable things you'd love to do, and do some each week. It's really important to have a lot of fun and try new things to replace the 'fun' you had getting wasted.
Set some challenging goals for yourself - working for a charity, paid work, education, mending the rift with family by offering to help them in some way that proves you are growing up. Or invite them for lunch and practise cooking a couple of nice recipes first so you feel confident.
Be kind to yourself if you have setbacks and blips. See the funny side of failure and get back on track with lots of self compassion.
Also, try some apps that block the internet for at least several hours a day when you'd usually be wasting time on TikTok. Use that time to get fit or learn a new skill.
You can also think about where you want your life to be in 5 years, then 3 years, then 1 year, 6 months, 3 months, 1 month, one week. You work backwards from 5 years to help yourself think about the impact of small actions you take now.