My main piece of advice that I write on every post about ADHD is the following: Get plenty of sleep, exercise, and look into meditating. Using the Waking Up app by Sam Harris has really taught me so much more than I was expecting. For the first time last year I went 3 months without medicine. I wanted to gauge how strong my attention/focus muscle was without medicine. At the end of 3 months I was able to start noticing when I was distracted or in my head and that was such a be improvement for me, because it allowed me to start paying attention again. I also noticed how I was communicating with myself. I went from being negative towards myself because I knew i should be paying attention. To understanding where my mind is at that day and knowing that today might be a harder day than yesterday, but that is okay. Just take it one step at a time.
TLDR: Exercise & Meditation. Mindfulness will help keep you present and away from the endless mind games you can experience with ADHD