I made a video about my approach here: https://www.youtube.com/watch?v=3hMVy4aKEZ4

But the gist of it is, you need to block distractions and be present in the moment, focusing on the task at hand. When I'm not feeling it, I use the Pomodoro Technique to get me started. Once the initial inertia is gone, I can keep going even without the technique.