Dude I'm 28 and I still struggle with all of that. I did some research and I'm trying again to establish a routine so I don't lose my teeth by the time I'm 40. I love spreadsheets and crossing things out and checking boxes, so I made a spreadsheet with a list of each day and brush teeth, tongue scrape, and mouthwash for the morning, and brush teeth, tongue scrape, floss, mouthwash for the evening. You want to do them in that order btw and not within 30 minutes of eating (before or after). But the hardest part for me is remembering to do it and getting the willpower to do it. For so many years I struggled with poor self image and still do and it was a pain to look in the mirror and I avoided showers and brushing my teeth even when I thought about it. It would literally take me an hour to get in the shower before I even turn the water on and sometimes I'd just be sitting there crying. I got a little more used to it eventually but I still only do it when it's bad enough to notice. Reminders don't work for me because I ignore them or tune them out. Get someone to keep after you, could be your parents like me, tell them to set a reminder for themselves but for them to not remind you but check if you actually did it or not. Once you get this going for a month or so every day, (in theory, I haven't gotten there yet) it should become a routine and you'll at least be used to going to the bathroom and doing your thing even if you may not feel like it. Then the only issue there is motivation. Keep an alarm or some kind of reminder for yourself and use something like a checklist to help motivate you and remind yourself how far you've come. The first week I got my parents to check on me I had brushed at least once a day for 6 out of 7 days which I haven't honestly done (this is gunna sound gross) in years.
Self esteem can be a major factor at any age but especially becoming an adult and so you need to actively work at it. Wash your face and ears in the shower while you're wet anyway. I hate getting wet, naked, or barefoot, but if you're already in the shower that parts done. Let the water in your ears and behind them and dry them after, and take a deep breath and do as much of one side of your face as you can under the showerhead including your forehead, nose (including under the nostril flares), behind your ears again, around your mouth, and your neck, then do it again for the other side. It's also a great way to waken up and clear out your sinuses in a hot shower lol
Something that I've been trying is to do 20-30 minutes of exercise on an exercise bike, then do my teeth routine, and take a shower before I do anything else (I play on my phone while on the bike). I don't work atm because I'm a full time student in grad school so it may be different for you with school or a job but I've heard it works best in the morning for attention and mood etc so I'm trying it out. So far I've been a lot more productive with my adhd (although I'm still on my phone a lot) and my depression is a little more manageable (still get mood swings though because of a recent med change) but I can feel my heart starting to improve because I'm severely out of shape and my teeth no longer look yellow and more off white and I need to find a dentist for a good cleaning. Sorry if this is kinda gross, hygiene always is, but I hope these tips help and let me know if you want more info