I've dealt with ADHD for 76 years. There are two practices that work for me.

1)Short-term (hours scale): Some tasks are helped by frequent changing focus, for example writing or painting. They permit non-linear work flow. Your progress is recorded up to the point when you pursue a worthwhile inspiration, and when you return to the task, you can quickly refresh your focus and continue. Perhaps this is why ADHD people are considered to be creative. They can make use of inspiration. If you can structure your effort into a way that preserves progress and facilitates re-focus later, this might work for you.

2)Long-term (days, weeks...): Here are 3 aspects that need to be addressed individually. A) Clearly define what you want to accomplish. Write it down. B) Plan exactly how you are going to accomplish your goal. Write it all down. Be explicit. C)Devise a scheme to periodically review each project for progress and identify the next step. Remind yourself why this task is worth pursuing.

Every morning I review my current long-term tasks in this way. I keep these tasks, their goals, their plans of attack, and why they are important in an outliner. Launching my outline is the first thing I do after my bath and brushing my teeth.

An anti-depressant helps quite a lot.

There are no silver bullets for this, and real-life is somewhat messier than I have described. But you can improve things by quite a bit if you persist.

Good luck.

The answer to this seems like it will depend on what your distractions are.

Without knowing that, I think my suggestion would be to be more deliberate with my time. By that I mean, set a timer for each thing you need to do, and only reward yourself with a distraction after you have focused successfully. Never reward yourself when you failed to focus.

Start small and increase the amount of focus you require of yourself over time.

In my experience, most self help books are not worth the paper they are printed on. For medical advice, I would start with sites like Harvard Health, Mayo Clinic, and Cleveland Clinic. These sites consistently stick to with the basics. I.e., lack of focus could be due to hundreds of factors. In order to give yourself the best chance, start out with the basics. (a) are you getting enough sleep? (b) are you eating healthy? (c) are you getting enough physical exercise? (d) how are your relationships? (e) are you financially stressed? (f) are you overwhelmed?

In other words, if you don't take care of yourself and feel you have things under control, no amount of willpower will let you focus.

Some people love to do everything to music, but I, for example, begin to lose focus while listening. Maybe you are more comfortable working while eating or smoking a cigarette? Or it's even simpler, and you just have lack of sleep or motivation. With the latter, unfortunately, you can not always do something, as in the case of studying at university in an uninteresting field of study.

The main thing is not to blame yourself for procrastination. It has already been proven that most people are trapped by deadlines, and it's OK! Productivity increases when deadlines are tight.

Unplug:

- Disconnect from the internet

- Disconnect your laptop from the charger and try to ship whatever you're working on uniquely on the laptop's charge.

These are artificial handicaps but when I do it, damn. You're looking at that battery charge and you prioritize ruthlessly. This is great to ship proof of concepts, prototypes, etc.

procastinate too much to the point that it hurts so much. focus comes naturally at that point, along with deterioration.

Nothing beats cutting down on distractions.