ADHD/Bipolar here, I really struggle with this, and using external tools is not an option, for me is just more multitasking risk!,something that works for me, aside from the drugs and good sleep, is a top down approach when programming, I just implement functions in terms of undefined magic functions/objects (all red in the IDE!) and start backwards implementing them, I used this "technique" when I was a Java developer using IntelliJ (CTRL+SPACE over undefined item -> implement). that kept my attention in easy chunks and well defined tasks. Type driven development is another "technique" I discovered, and it worked very well for me lately. Using the compiler as your guide and friend.