Creating the conditions for intentional action...

Here are the things that help me. You can find alternatives that work for you.

1. Use a visual timer. Either use the Clock app or use the Time Timer app. Better still, buy a physical analog timer. Your focus is significantly different when you have a visual timer in front of your eyes.
2. 90 minutes focus, 30 minutes rest. Dr. Andrew Huberman talks about the ultradian cycles of 90 minutes which happen not only during our sleep but also while we are awake. We can start an ultradian cycle at any time, we don't have to catch it. But it would last 90 minutes. So, focus for 90 minutes and then rest for 30 minutes. For resting, I use the 20-minutes NSDR that Dr. Huberman has so generously recorded. You can start with the 10-minute one also.
3. Brain.fm and noise cancelling earphones. I get distracted by random sounds as my nervous system is very sensitive. I have found the focus music on brain.fm as one of the effective ways that allows me to go deep into my work. The recharge or destress music is good for resting too.
4. Offline mode: Tim Ferriss once said that the most effective productivity app comes by default on your phone and is called Airplane mode. Unless you need the internet for a particular task, go offline. So much so, try to make it so that you need to get up physically in order to turn it back on.
5. Putting the phone away: The world will not come to an end if you don't respond to your iMessages, WhatsApp, Instagram and all for a few hours. Tell your friends that your phone is not with you when you are working and they would get used to it sooner or later.
6. Dark mode & grayscale: I prefer writing in the dark mode on my computer. It helps me be less distracted. An even more effective setting is Grayscale. You can find it in the Accessibility settings and then you can use the shortcut to turn it on or off.
7. Boundaries: I set 3 pm as a boundary for deep work. No meetings, phone calls before 3 pm. After that, I can only wrap up the minimum stuff that needs to be done. That allows me to focus from the morning until that time.
8. Small losses: Something might get missed when you are working. An Amazon delivery guy will go back without delivering your package. A friend would be in the neighbourhood and would miss you because you didn't respond. Be okay with small losses if you want the big wins.
9. Notepad: When you are working on something, suddenly the idea of ordering something on Amazon would strike you. And it would be tempting to order it immediately. It would only take a couple of minutes. But that's a slippery slope. That allows resistance to slip in and take over. Instead, keep a notepad handy. Write down these ideas and once you are done with your deep work, choose whether you want to move ahead with them or not.
10. Maintain your seat. Do not leave your seat. Not for coffee. Not for anything. As much as you can avoid it, keep maintaining your seat. I can't emphasise this one enough. When the 90 minutes are over, you can go and do whatever it was that was making you leave the seat.
11. The most important skill is to restart, is to regain your focus when you get distracted. All the above would break, sooner or later, but can you learn to get back to your work, your task, your action? The more you do it, the more you would get better at it.