I also have a hard time with this, and I have ADD too. I love love love planning projects and being creative, thinking up new ideas, but the action - well - not so much. My therapist asked me to read a book and find my Enneagram type. I am a seven, The Enthusiast. I think I feel satisfied just by having a thought of something to do, rather than actually doing it.
I love the book: Getting Things Done, The Art of Productivity. It taught me an essential fact: You have to think of the exact next step in a project before you can move it forwards. You can write the project down (Post It note), and have categories :At home, at phone, at computer, on errands, waiting for info from somebody. Move the Post It around as needed.
The Post-it method didn't work so well for me, but I am having a lot of luck using a gmail star approach. As an email comes in, I assign it a colored star to put it in the correct inbox (you can have multiple inboxes with gmail, all shown above a main inbox. My inboxes are: At home, At Work, Ask someone, Waiting for info, Errand. Once an item is completed, I un-star it, and move it to Reference/Actioned. I have a horrible memory, so it helps if I am demotivated (and before I meet weekly with my boss) to review my Actioned emails, to remind myself of what I have accomplished.
I first had to move 2000 emails out of my inbox, and just created a reference label for them. Now, if I am at home, I know I can only action the green items on my email list. When I am at work, I try to just do the orange items, since I have a limited time in the office, and I try not to go in too much.
I need to be disciplined with the stars, but it really forces me to really think about what my next step is. It helps me stay focused too, since I have smaller groups of emails to manage, and I typically get overwhelmed and anxious very easily. I now send emails to myself, since gmail has become my one and only to-do list. It helps that I can access this on my phone.
For paper, I carry around manila folders, with specific project headings on them. I have a handbag/laptop bag that zips all the way down so it's easier for me to stay organized and find things (very forgetful and lose things all the time). I have corresponding hanging file folders at home, so as projects are finished, they are supposed to be filed (still working on that, my bag is really heavy right now.)
I hope I have helped somewhat. Good Luck!