Some thoughts:

Mindset:

• Medication will not make you better at performing a routine. What I've learned is, we are bad at that because we never developed the skills to keep a routine when we were kids, which is a result of our ADHD going undiagnosed and our parents not having the information they needed to guide us.
• Guilt will prevent you from doing a routine and will not motivate you to do it.
• Your internal monolog is important, the way you talk about your routine to yourself will impact your ability to do it. Having ADHD means you are also riddled with shame, shame others have placed on you. That shame becomes your internal monolog. You have to resist belittling yourself, and you have to actually say positive things, encouraging things, even if you feel like you are faking it. Don't just say them in your head, say them out loud, say them in the car, say them in the mirror after you wake up.

Practical:

• You should know that it can take between 18 and 254 days for a person to form a new habit. On average, 66 days before the habit becomes automatic.
• Try Piggy Backing: Often times you can piggyback another task onto something you already do all the time. Think of the things you know you do already, and use that as a hack to do the other things too. If you use the bathroom right as you get home every day, just brush your teeth right after. Brushing and then eating afterward is mostly fine and way better than never brushing.
• Start small: You can't build 100 habits all at once, that's never going to work. Pick one or two and just zero in on them. Once they begin to feel "automatic", or, it feels weird to skip them, then you can try and tackle another.
• Check out the Loop Habit Tracker app for your phone (android). I constantly use this thing. The reason I like it, and the reason it works for me, are two things. 1) Everything you schedule in the app appears as a notification that cannot be swiped away or cleared away with the "Clear All" button. 2) You name your task in the form of a question, "Did you brush your teeth today?", and the notification has two buttons "Yes" or "No". This act of acknowledging that I either did, or did not do something, makes me want to do it next time. This app might not work for you, but it does for me. I set these daily tasks to show up around the time I might be waking up or going to bed. They pile up in the notification window and are very annoying to get rid of. The most satisfying way to get rid of them is to just do the task.
• Externalizing: Keeping things on your phone is a hit or miss experience. My phone, like my fridge, is a black box and I have no idea what is in it ever. Keeping lists on my phone is great until there is no rewarding reason to open the note's app. That is the issue with all this note-taking, is there is no real reward for doing any of it at the moment. Delayed gratification is not something our brains give a shit about. What I find works for me is a big ass white board. I keep the white board in the highest trafficked part of my house, so that it's very difficult to avoid. I use it mostly as long-term storage for things I might forget.
• Know your triggers: When I get home, if I change out of my work cloths into my comfortable at home cloths, I know it will act as a trigger to send me into "lounge mode". Something about keeping my shoes on and keeping my work cloths on helps me maintain that momentum I had from work, and allows me to do a few things before I "settle in". This might be taking out the trash in the house, cleaning the litter box, doing dishes, making dinner, etc. Sometimes my kid will say to me "Dad, you still have your shoes on." and I always tell her "It's because I want to get things done."
• If you can, use the buddy system: At some point, I told my wife, that it would greatly help me get into the habit of doing nightly hygiene stuff if we did it together. She eventually agreed, after not really understanding why, and would make sure we both brushed our teeth at the same time. Now, even on my own, I can't go to bed without brushing. This is a good hack for kids too, now me and my kiddo brush our teeth together every night.

Lastly, just read up on the science of habits. Knowing that there is a clear understanding of how habits get formed, and why, you can leverage that knowledge for yourself. We obviously have a much harder time doing this, but this science still applies to us as well.