my son has ADHD and gets very frustrated when he has to write essays, reports, etc.
i found that one thing that helped him a lot was to put individual facts or topics on 3x5 index cards as he thought of them
that way you don't have to work your way through it in a straight line
once your ideas are on the cards, you can shuffle them around until you have them in the order you want to use and throw away the ones you don't want to use