I don't have ADHD (that I know of), but often struggle with the "activation" bit as well. One seemingly simple thing that's really, really helped me was a quote

I don't have ADHD (that I know of), but often struggle with the "activation" bit as well. One seemingly simple thing that's really, really helped me was a quote from Jerry Seinfeld (on the Tim Ferriss podcast): "You don't have to write, but you can't do anything else." Replace "write" with "code" or whatever you need to do. His process was to set a fixed amount of time to work (having a defined length is important), sit down, start the timer, and either write or sit and do nothing. Removing the mental pressure of "oh no I have to get this thing done" by making _doing nothing_ an acceptable outcome was huge for me. It took a few tries to actually stick to the "do nothing else" part--no HN, no phones, etc--but now I find I can dispense with distractions and get work done much more easily.