1. Get your health/medication on point. Find out what medication works for your and take it consistently. You can't afford to lose out on the extra executive function good medication can give you.
2. Accept your ADHD. Flagellating yourself for missed deadlines, forgotten tasks, procrastination and so on will only make things worse. I used to beat myself up about procrastination and it led to a cycle of anxiety that only made things worse. If you have a low productivity day accept it. Take each new day, each new project and each new task as completely fresh an isolated.
3. Record yourself working. Use a camera or a screen recorder. Try to notice exactly what happens. Do you start a task and then procrastinate? Do you procrastinate before the task starts? What triggers it? Is it internal? External? It can feel like you know what is triggering things but getting an actual recording can show you things you would have never noticed in the moment.
4. Inject novelty into boring tasks. Often simple boring tasks don't have enough excitement to make them interesting. Counterintuitively, making a task more difficult can add novelty and help stop you procrastinating. What adds novelty and challenge will be very individual.
5. Make peace with that fact that some techniques will stop working for you and you will need to change how you work. Just because something was working great last week doesn't mean it will work this week.
Good luck!