I use lists, a lot of them. I have Daily, Weekly, and Yearly lists (all on paper). I don't have them to be productive, I have them so that I don't have to remember the things on the lists. I want my head to be empty of all the things I cannot do right now. For me, the best way to achieve that, is to write the things I want to do in the future. That way, they get out of my head and I can focus on my daily business.

For me, the same trick also works for other things that are on my mind. Especially the things that would usually keep me up at night. I write them down, so that they get out of my head.