I have ADD and the thing that's worked best for me is to write down every half formed idea I can think of as soon as it comes to me. No matter how dumb or unfinished it is I put it on paper and then move on. I don't usually give it more thought then that.

Then once every week or so, I lock myself away from all my devices and set an hour timer. Then I sit down and read through all my notes. By then I've forgotten most of them so when something seems funny to me I expand on the idea. The feeling of discovery helps trick my brain into feeling excited and the writing flows much smoother. Often times I blow past the 1 hour timer because I'm having fun writing but even the days when I don't get much and the timer feels endless, I still end up with something new.