Seriously. After 15 years of struggling with various self help programs, an ADHD-PI diagnosis and medication fixed 90% of my problems. I feel like that movie Limitless was inspired by someone who really needed ADHD medication and finally got it.
Yes: Hydration is a little important. Sleep is very important (white noise machine, blackout curtains, melatonin when needed, regular schedule, no alcohol near bedtime on work nights.) Exercise is a little important, but too much is detrimental. Learning meditation, specifically body-scan, was really helpful for me though indirectly. It helped me better notice my internal states, which then helps me remove blockers to focusing. A low-carb diet also helped, but is rather high-effort to maintain so I don't follow it anymore. I make great use of reminders on my phone, and appointments on my calendar, because I have no faith in my ability to remember things at the right times despite having a great memory.
I wouldn't pay too much attention to the "tiers". Consider it a general list of things that may be helpful, and assume that the relative importance of each is likely to be different for you.
I agree with this comment, but with the addition that sleep quality is very important if you don't have it. If your sleep is pretty close to optimal already, you may not notice a slight improvement.
I agree - I think sleep is the only universal here. I find different things may help at different times, too, or become more important to counter different external stressors and anxieties.
I've never found exercise to be a particularly important part of my mental health, but in lockdown I've become utterly dependent on it. It provides routine, structure, control and a sense of progress - all of which I was getting more of in other places before but which I'm now lacking without the exercise.
I would previously really push hard on exercise looking for some magic result, and I found it made my concentration worse because my body is trying to recover from the previous day's workout. It's good for stress relief though. Just find the right amount for your body, it will be more than zero but less than some threshold.
