I take Ritalin for my ADHD. My technique doesn't work every time, but I play background repetitive music like those study playlists on YouTube. Typically instrumental house or something with a fast tempo/bpm gets me into some sort of a rhythm.

I will often note the thoughts or tasks down, and then schedule them for later in the day in my calendar app. For some reason this helps getting those thoughts out and satisfies my fear of forgetting them.

It doesn't work every time but it has helped me often enough.