How to stay focused for long periods of time?

Identify your distractions: Start by identifying the things that tend to distract you and distract you from your work. This could be anything from social media notifications to loud noises to hunger. Once you know what your distractions are, you can take steps to minimize or eliminate them.

Set goals and priorities: Set clear goals and priorities for your work, and focus on completing the most important tasks first. This will help you stay focused and avoid getting sidetracked by less important tasks.

Create a conducive environment: Create a conducive environment for focused work, with minimal distractions and comfortable surroundings. This could mean working in a quiet, distraction-free space, or using noise-canceling headphones to block out external noise.

Take regular breaks: Take regular breaks to refresh your mind and avoid burnout. This could mean taking a short walk, stretching, or engaging in a mindfulness exercise to clear your mind and refocus.

Use technology to your advantage: Use technology to your advantage by using tools and apps that can help you stay focused and avoid distractions. For example, you could use a productivity app that blocks distracting websites, or a time-tracking app that helps you manage your time effectively.

The "long periods of time" part got my attention...

Usually the most difficult part is to get started, but just questions seems to suggest that is not hard for you to get started, rather than keep going.

Do you like the thing you are supposed to focus on? Because IMO, there is no substitute for sustainable focus if you don't like something (or you aren't forced).

I'm not sure what's motivating this question, but I've asked it myself at times and that search led me to my doctor and to an ADHD diagnosis and stimulant prescription (Vyvanse). For me personally, less stress (both in how I dealt with things, the expectations I put on myself, and asking for and receiving more help from others) seems to have done more than the medication, which I no longer take. Again, anecdotally, omega 3 and l-tyrosine supplementation have had positive effects as well.